Framework to build dane support

10 files changed, 1418 insertions, 1 deletions

diff --git a/doc/doc-txt/OptionLists.txt b/doc/doc-txt/OptionLists.txt
index ef6195600..375850d6b 100644
--- a/doc/doc-txt/OptionLists.txt
+++ b/doc/doc-txt/OptionLists.txt
@@ -181,6 +181,7 @@ dns_check_names_pattern              string          +             main
 dns_csa_search_limit                 integer         5             main              4.60
 dns_csa_use_reverse                  boolean         true          main              4.60
 dns_dnssec_ok                        integer         -1            main              4.82
+dns_dane_ok                          integer         -1            main              4.83
 dns_ipv4_lookup                      boolean         false         main              3.20
 dns_qualify_single                   boolean         true          smtp
 dns_retrans                          time            0s            main              1.60
diff --git a/src/OS/Makefile-Base b/src/OS/Makefile-Base
index 87a803704..8937f3cad 100644
--- a/src/OS/Makefile-Base
+++ b/src/OS/Makefile-Base
@@ -298,7 +298,7 @@ convert4r4: Makefile ../src/convert4r4.src
 
 OBJ_WITH_CONTENT_SCAN = malware.o mime.o regex.o spam.o spool_mbox.o
 OBJ_WITH_OLD_DEMIME = demime.o
-OBJ_EXPERIMENTAL = bmi_spam.o spf.o srs.o dcc.o dmarc.o
+OBJ_EXPERIMENTAL = bmi_spam.o spf.o srs.o dcc.o dmarc.o dane.o
 
 # Targets for final binaries; the main one has a build number which is
 # updated each time. We don't bother with that for the auxiliaries.
@@ -541,6 +541,7 @@ acl.o:           $(HDRS) acl.c
 child.o:         $(HDRS) child.c
 crypt16.o:       $(HDRS) crypt16.c
 daemon.o:        $(HDRS) daemon.c
+dane.o:          $(HDRS) dane.c dane-gnu.c dane-openssl.c
 dbfn.o:          $(HDRS) dbfn.c
 debug.o:         $(HDRS) debug.c
 deliver.o:       $(HDRS) deliver.c
diff --git a/src/scripts/MakeLinks b/src/scripts/MakeLinks
index 01cd21f1c..a50f75b36 100755
--- a/src/scripts/MakeLinks
+++ b/src/scripts/MakeLinks
@@ -271,6 +271,10 @@ ln -s ../src/srs.c             srs.c
 ln -s ../src/srs.h             srs.h
 ln -s ../src/dcc.c             dcc.c
 ln -s ../src/dcc.h             dcc.h
+ln -s ../src/dane.c            dane.c
+ln -s ../src/dane-gnu.c        dane-gnu.c
+ln -s ../src/dane-openssl.c    dane-openssl.c
+ln -s ../src/danessl.h         danessl.h
 
 
 # End of MakeLinks
diff --git a/src/src/config.h.defaults b/src/src/config.h.defaults
index ba4615c11..49ab276ff 100644
--- a/src/src/config.h.defaults
+++ b/src/src/config.h.defaults
@@ -168,6 +168,7 @@ it's a default value. */
 /* EXPERIMENTAL features */
 #define EXPERIMENTAL_BRIGHTMAIL
 #define EXPERIMENTAL_CERTNAMES
+#define EXPERIMENTAL_DANE
 #define EXPERIMENTAL_DCC
 #define EXPERIMENTAL_DMARC
 #define EXPERIMENTAL_DSN
diff --git a/src/src/dane-gnu.c b/src/src/dane-gnu.c
new file mode 100644
index 000000000..b98bffad6
--- /dev/null
+++ b/src/src/dane-gnu.c
@@ -0,0 +1,21 @@
+/*************************************************
+*     Exim - an Internet mail transport agent    *
+*************************************************/
+
+/* Copyright (c) University of Cambridge 1995 - 2013 */
+/* See the file NOTICE for conditions of use and distribution. */
+
+/* This file (will) provide DANE support for Exim using the GnuTLS library,
+but is not yet an available supported implementation.  This file is #included
+into dane.c when USE_GNUTLS has been set.  */
+
+/* As of March 2014, the reference implementation for DANE that we are
+using was written by Viktor Dukhovny and it supports OpenSSL only.  At
+some point we will add GnuTLS support, but for right now just abort the
+build and explain why. */
+
+
+#error No support for DANE using GnuTLS yet.
+
+
+/* End of dane-gnu.c */
diff --git a/src/src/dane-openssl.c b/src/src/dane-openssl.c
new file mode 100644
index 000000000..790b4f079
--- /dev/null
+++ b/src/src/dane-openssl.c
@@ -0,0 +1,1306 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdint.h>
+
+#include <openssl/opensslv.h>
+#include <openssl/err.h>
+#include <openssl/crypto.h>
+#include <openssl/safestack.h>
+#include <openssl/objects.h>
+#include <openssl/x509.h>
+#include <openssl/x509v3.h>
+#include <openssl/evp.h>
+
+#if OPENSSL_VERSION_NUMBER < 0x1000000fL
+#error "OpenSSL 1.0.0 or higher required"
+#else
+
+#include "danessl.h"
+
+#define DANE_F_ADD_SKID                 100
+#define DANE_F_CHECK_END_ENTITY         101
+#define DANE_F_GROW_CHAIN               102
+#define DANE_F_LIST_ALLOC               103
+#define DANE_F_MATCH                    104
+#define DANE_F_PUSH_EXT                 105
+#define DANE_F_SET_TRUST_ANCHOR         106
+#define DANE_F_SSL_CTX_DANE_INIT        107
+#define DANE_F_SSL_DANE_ADD_TLSA        108
+#define DANE_F_SSL_DANE_INIT            109
+#define DANE_F_SSL_DANE_LIBRARY_INIT    110
+#define DANE_F_VERIFY_CERT              111
+#define DANE_F_WRAP_CERT                112
+
+#define DANE_R_BAD_CERT                 100
+#define DANE_R_BAD_CERT_PKEY            101
+#define DANE_R_BAD_DATA_LENGTH          102
+#define DANE_R_BAD_DIGEST               103
+#define DANE_R_BAD_NULL_DATA            104
+#define DANE_R_BAD_PKEY                 105
+#define DANE_R_BAD_SELECTOR             106
+#define DANE_R_BAD_USAGE                107
+#define DANE_R_DANE_INIT                108
+#define DANE_R_DANE_SUPPORT             109
+#define DANE_R_LIBRARY_INIT             110
+#define DANE_R_NOSIGN_KEY               111
+#define DANE_R_SCTX_INIT                112
+
+#ifndef OPENSSL_NO_ERR
+#define DANE_F_PLACEHOLDER              0               /* FIRST! Value TBD */
+static ERR_STRING_DATA dane_str_functs[] = {
+    {DANE_F_PLACEHOLDER,                "DANE library"},        /* FIRST!!! */
+    {DANE_F_ADD_SKID,                   "add_skid"},
+    {DANE_F_CHECK_END_ENTITY,           "check_end_entity"},
+    {DANE_F_GROW_CHAIN,                 "grow_chain"},
+    {DANE_F_LIST_ALLOC,                 "list_alloc"},
+    {DANE_F_MATCH,                      "match"},
+    {DANE_F_PUSH_EXT,                   "push_ext"},
+    {DANE_F_SET_TRUST_ANCHOR,           "set_trust_anchor"},
+    {DANE_F_SSL_CTX_DANE_INIT,          "SSL_CTX_dane_init"},
+    {DANE_F_SSL_DANE_ADD_TLSA,          "SSL_dane_add_tlsa"},
+    {DANE_F_SSL_DANE_INIT,              "SSL_dane_init"},
+    {DANE_F_SSL_DANE_LIBRARY_INIT,      "SSL_dane_library_init"},
+    {DANE_F_VERIFY_CERT,                "verify_cert"},
+    {DANE_F_WRAP_CERT,                  "wrap_cert"},
+    {0,                                 NULL}
+};
+static ERR_STRING_DATA dane_str_reasons[] = {
+    {DANE_R_BAD_CERT,           "Bad TLSA record certificate"},
+    {DANE_R_BAD_CERT_PKEY,      "Bad TLSA record certificate public key"},
+    {DANE_R_BAD_DATA_LENGTH,    "Bad TLSA record digest length"},
+    {DANE_R_BAD_DIGEST,         "Bad TLSA record digest"},
+    {DANE_R_BAD_NULL_DATA,      "Bad TLSA record null data"},
+    {DANE_R_BAD_PKEY,           "Bad TLSA record public key"},
+    {DANE_R_BAD_SELECTOR,       "Bad TLSA record selector"},
+    {DANE_R_BAD_USAGE,          "Bad TLSA record usage"},
+    {DANE_R_DANE_INIT,          "SSL_dane_init() required"},
+    {DANE_R_DANE_SUPPORT,       "DANE library features not supported"},
+    {DANE_R_LIBRARY_INIT,       "SSL_dane_library_init() required"},
+    {DANE_R_SCTX_INIT,          "SSL_CTX_dane_init() required"},
+    {DANE_R_NOSIGN_KEY,         "Certificate usage 2 requires EC support"},
+    {0,                         NULL}
+};
+#endif
+
+#define DANEerr(f, r) ERR_PUT_error(err_lib_dane, (f), (r), __FILE__, __LINE__)
+
+static int err_lib_dane = -1;
+static int dane_idx = -1;
+
+#ifdef X509_V_FLAG_PARTIAL_CHAIN       /* OpenSSL >= 1.0.2 */
+static int wrap_to_root = 0;
+#else
+static int wrap_to_root = 1;
+#endif
+
+static void (*cert_free)(void *) = (void (*)(void *)) X509_free;
+static void (*pkey_free)(void *) = (void (*)(void *)) EVP_PKEY_free;
+
+typedef struct dane_list {
+    struct dane_list *next;
+    void *value;
+} *dane_list;
+
+#define LINSERT(h, e) do { (e)->next = (h); (h) = (e); } while (0)
+
+typedef struct DANE_HOST_LIST {
+    struct DANE_HOST_LIST *next;
+    char *value;
+} *DANE_HOST_LIST;
+
+typedef struct dane_data {
+    size_t datalen;
+    unsigned char data[0];
+} *dane_data;
+
+typedef struct DANE_DATA_LIST {
+    struct DANE_DATA_LIST *next;
+    dane_data value;
+} *DANE_DATA_LIST;
+
+typedef struct dane_mtype {
+    int mdlen;
+    const EVP_MD *md;
+    DANE_DATA_LIST data;
+} *dane_mtype;
+
+typedef struct DANE_MTYPE_LIST {
+    struct DANE_MTYPE_LIST *next;
+    dane_mtype value;
+} *DANE_MTYPE_LIST;
+
+typedef struct dane_selector {
+    uint8_t selector;
+    DANE_MTYPE_LIST mtype;
+} *dane_selector;
+
+typedef struct DANE_SELECTOR_LIST {
+    struct DANE_SELECTOR_LIST *next;
+    dane_selector value;
+} *DANE_SELECTOR_LIST;
+
+typedef struct DANE_PKEY_LIST {
+    struct DANE_PKEY_LIST *next;
+    EVP_PKEY *value;
+} *DANE_PKEY_LIST;
+
+typedef struct DANE_CERT_LIST {
+    struct DANE_CERT_LIST *next;
+    X509 *value;
+} *DANE_CERT_LIST;
+
+typedef struct SSL_DANE {
+    int            (*verify)(X509_STORE_CTX *);
+    STACK_OF(X509) *roots;
+    STACK_OF(X509) *chain;
+    const char     *thost;              /* TLSA base domain */
+    char           *mhost;              /* Matched, peer name */
+    DANE_PKEY_LIST pkeys;
+    DANE_CERT_LIST certs;
+    DANE_HOST_LIST hosts;
+    DANE_SELECTOR_LIST selectors[SSL_DANE_USAGE_LAST + 1];
+    int            depth;
+    int            multi;               /* Multi-label wildcards? */
+    int            count;               /* Number of TLSA records */
+} SSL_DANE;
+
+#ifndef X509_V_ERR_HOSTNAME_MISMATCH
+#define X509_V_ERR_HOSTNAME_MISMATCH X509_V_ERR_APPLICATION_VERIFICATION
+#endif
+
+static int match(DANE_SELECTOR_LIST slist, X509 *cert, int depth)
+{
+    int matched;
+
+    /*
+     * Note, set_trust_anchor() needs to know whether the match was for a
+     * pkey digest or a certificate digest.  We return MATCHED_PKEY or
+     * MATCHED_CERT accordingly.
+     */
+#define MATCHED_CERT (SSL_DANE_SELECTOR_CERT + 1)
+#define MATCHED_PKEY (SSL_DANE_SELECTOR_SPKI + 1)
+
+    /*
+     * Loop over each selector, mtype, and associated data element looking
+     * for a match.
+     */
+    for (matched = 0; !matched && slist; slist = slist->next) {
+        DANE_MTYPE_LIST m;
+        unsigned char mdbuf[EVP_MAX_MD_SIZE];
+        unsigned char *buf;
+        unsigned char *buf2;
+        unsigned int len;
+
+        /*
+         * Extract ASN.1 DER form of certificate or public key.
+         */
+        switch (slist->value->selector) {
+        case SSL_DANE_SELECTOR_CERT:
+            len = i2d_X509(cert, NULL);
+            buf2 = buf = (unsigned char *) OPENSSL_malloc(len);
+            if (buf)
+                i2d_X509(cert, &buf2);
+            break;
+        case SSL_DANE_SELECTOR_SPKI:
+            len = i2d_X509_PUBKEY(X509_get_X509_PUBKEY(cert), NULL);
+            buf2 = buf = (unsigned char *) OPENSSL_malloc(len);
+            if (buf)
+                i2d_X509_PUBKEY(X509_get_X509_PUBKEY(cert), &buf2);
+            break;
+        }
+
+        if (buf == NULL) {
+            DANEerr(DANE_F_MATCH, ERR_R_MALLOC_FAILURE);
+            return 0;
+        }
+        OPENSSL_assert(buf2 - buf == len);
+
+        /*
+         * Loop over each mtype and data element
+         */
+        for (m = slist->value->mtype; !matched && m; m = m->next) {
+            DANE_DATA_LIST d;
+            unsigned char *cmpbuf = buf;
+            unsigned int cmplen = len;
+
+            /*
+             * If it is a digest, compute the corresponding digest of the
+             * DER data for comparison, otherwise, use the full object.
+             */
+            if (m->value->md) {
+                cmpbuf = mdbuf;
+                if (!EVP_Digest(buf, len, cmpbuf, &cmplen, m->value->md, 0))
+                    matched = -1;
+            }
+            for (d = m->value->data; !matched && d; d = d->next)
+                if (cmplen == d->value->datalen &&
+                    memcmp(cmpbuf, d->value->data, cmplen) == 0)
+                    matched = slist->value->selector + 1;
+        }
+
+        OPENSSL_free(buf);
+    }
+
+    return matched;
+}
+
+static int push_ext(X509 *cert, X509_EXTENSION *ext)
+{
+    X509_EXTENSIONS *exts;
+
+    if (ext) {
+        if ((exts = cert->cert_info->extensions) == 0)
+            exts = cert->cert_info->extensions = sk_X509_EXTENSION_new_null();
+        if (exts && sk_X509_EXTENSION_push(exts, ext))
+            return 1;
+        X509_EXTENSION_free(ext);
+    }
+    DANEerr(DANE_F_PUSH_EXT, ERR_R_MALLOC_FAILURE);
+    return 0;
+}
+
+static int add_ext(X509 *issuer, X509 *subject, int ext_nid, char *ext_val)
+{
+    X509V3_CTX v3ctx;
+
+    X509V3_set_ctx(&v3ctx, issuer, subject, 0, 0, 0);
+    return push_ext(subject, X509V3_EXT_conf_nid(0, &v3ctx, ext_nid, ext_val));
+}
+
+static int set_serial(X509 *cert, AUTHORITY_KEYID *akid, X509 *subject)
+{
+    int ret = 0;
+    BIGNUM *bn;
+
+    if (akid && akid->serial)
+        return (X509_set_serialNumber(cert, akid->serial));
+
+    /*
+     * Add one to subject's serial to avoid collisions between TA serial and
+     * serial of signing root.
+     */
+    if ((bn = ASN1_INTEGER_to_BN(X509_get_serialNumber(subject), 0)) != 0
+        && BN_add_word(bn, 1)
+        && BN_to_ASN1_INTEGER(bn, X509_get_serialNumber(cert)))
+        ret = 1;
+
+    if (bn)
+        BN_free(bn);
+    return ret;
+}
+
+static int add_akid(X509 *cert, AUTHORITY_KEYID *akid)
+{
+    int nid = NID_authority_key_identifier;
+    ASN1_STRING *id;
+    unsigned char c = 0;
+    int ret = 0;
+
+    /*
+     * 0 will never be our subject keyid from a SHA-1 hash, but it could be
+     * our subject keyid if forced from child's akid.  If so, set our
+     * authority keyid to 1.  This way we are never self-signed, and thus
+     * exempt from any potential (off by default for now in OpenSSL)
+     * self-signature checks!
+     */
+    id = (ASN1_STRING *) ((akid && akid->keyid) ? akid->keyid : 0);
+    if (id && M_ASN1_STRING_length(id) == 1 && *M_ASN1_STRING_data(id) == c)
+        c = 1;
+
+    if ((akid = AUTHORITY_KEYID_new()) != 0
+        && (akid->keyid = ASN1_OCTET_STRING_new()) != 0
+        && M_ASN1_OCTET_STRING_set(akid->keyid, (void *) &c, 1)
+        && X509_add1_ext_i2d(cert, nid, akid, 0, X509V3_ADD_APPEND))
+        ret = 1;
+    if (akid)
+        AUTHORITY_KEYID_free(akid);
+    return ret;
+}
+
+static int add_skid(X509 *cert, AUTHORITY_KEYID *akid)
+{
+    int nid = NID_subject_key_identifier;
+
+    if (!akid || !akid->keyid)
+        return add_ext(0, cert, nid, "hash");
+    return X509_add1_ext_i2d(cert, nid, akid->keyid, 0, X509V3_ADD_APPEND) > 0;
+}
+
+static X509_NAME *akid_issuer_name(AUTHORITY_KEYID *akid)
+{
+    if (akid && akid->issuer) {
+        int     i;
+        GENERAL_NAMES *gens = akid->issuer;
+
+        for (i = 0; i < sk_GENERAL_NAME_num(gens); ++i) {
+            GENERAL_NAME *gn = sk_GENERAL_NAME_value(gens, i);
+
+            if (gn->type == GEN_DIRNAME)
+                return (gn->d.dirn);
+        }
+    }
+    return 0;
+}
+
+static int set_issuer_name(X509 *cert, AUTHORITY_KEYID *akid)
+{
+    X509_NAME *name = akid_issuer_name(akid);
+
+    /*
+     * If subject's akid specifies an authority key identifer issuer name, we
+     * must use that.
+     */
+    if (name)
+        return X509_set_issuer_name(cert, name);
+    return X509_set_issuer_name(cert, X509_get_subject_name(cert));
+}
+
+static int grow_chain(SSL_DANE *dane, int trusted, X509 *cert)
+{
+    STACK_OF(X509) **xs = trusted ? &dane->roots : &dane->chain;
+    static ASN1_OBJECT *serverAuth = 0;
+
+#define UNTRUSTED 0
+#define TRUSTED 1
+
+    if (trusted && serverAuth == 0 &&
+       (serverAuth = OBJ_nid2obj(NID_server_auth)) == 0) {
+        DANEerr(DANE_F_GROW_CHAIN, ERR_R_MALLOC_FAILURE);
+        return 0;
+    }
+    if (!*xs && (*xs = sk_X509_new_null()) == 0) {
+        DANEerr(DANE_F_GROW_CHAIN, ERR_R_MALLOC_FAILURE);
+        return 0;
+    }
+
+    if (cert) {
+        if (trusted && !X509_add1_trust_object(cert, serverAuth))
+            return 0;
+        CRYPTO_add(&cert->references, 1, CRYPTO_LOCK_X509);
+        if (!sk_X509_push(*xs, cert)) {
+            X509_free(cert);
+            DANEerr(DANE_F_GROW_CHAIN, ERR_R_MALLOC_FAILURE);
+            return 0;
+        }
+    }
+    return 1;
+}
+
+static int wrap_issuer(
+        SSL_DANE *dane,
+        EVP_PKEY *key,
+        X509 *subject,
+        int depth,
+        int top
+)
+{
+    int ret = 1;
+    X509 *cert = 0;
+    AUTHORITY_KEYID *akid;
+    X509_NAME *name = X509_get_issuer_name(subject);
+    EVP_PKEY *newkey = key ? key : X509_get_pubkey(subject);
+
+#define WRAP_MID 0              /* Ensure intermediate. */
+#define WRAP_TOP 1              /* Ensure self-signed. */
+
+    if (name == 0 || newkey == 0 || (cert = X509_new()) == 0)
+        return 0;
+
+    /*
+     * Record the depth of the trust-anchor certificate.
+     */
+    if (dane->depth < 0)
+        dane->depth = depth + 1;
+
+    /*
+     * XXX: Uncaught error condition:
+     *
+     * The return value is NULL both when the extension is missing, and when
+     * OpenSSL rans out of memory while parsing the extension.
+     */
+    ERR_clear_error();
+    akid = X509_get_ext_d2i(subject, NID_authority_key_identifier, 0, 0);
+    /* XXX: Should we peek at the error stack here??? */
+
+    /*
+     * If top is true generate a self-issued root CA, otherwise an
+     * intermediate CA and possibly its self-signed issuer.
+     *
+     * CA cert valid for +/- 30 days
+     */
+    if (!X509_set_version(cert, 2)
+        || !set_serial(cert, akid, subject)
+        || !X509_set_subject_name(cert, name)
+        || !set_issuer_name(cert, akid)
+        || !X509_gmtime_adj(X509_get_notBefore(cert), -30 * 86400L)
+        || !X509_gmtime_adj(X509_get_notAfter(cert), 30 * 86400L)
+        || !X509_set_pubkey(cert, newkey)
+        || !add_ext(0, cert, NID_basic_constraints, "CA:TRUE")
+        || (!top && !add_akid(cert, akid))
+        || !add_skid(cert, akid)
+        || (!top && wrap_to_root &&
+            !wrap_issuer(dane, newkey, cert, depth, WRAP_TOP))) {
+        ret = 0;
+    }
+    if (akid)
+        AUTHORITY_KEYID_free(akid);
+    if (!key)
+        EVP_PKEY_free(newkey);
+    if (ret) {
+        if (!top && wrap_to_root)
+            ret = grow_chain(dane, UNTRUSTED, cert);
+        else
+            ret = grow_chain(dane, TRUSTED, cert);
+    }
+    if (cert)
+        X509_free(cert);
+    return ret;
+}
+
+static int wrap_cert(SSL_DANE *dane, X509 *tacert, int depth)
+{
+    if (dane->depth < 0)
+        dane->depth = depth + 1;
+
+    /*
+     * If the TA certificate is self-issued, or need not be, use it directly.
+     * Otherwise, synthesize requisuite ancestors.
+     */
+    if (!wrap_to_root
+        || X509_check_issued(tacert, tacert) == X509_V_OK)
+        return grow_chain(dane, TRUSTED, tacert);
+
+    if (wrap_issuer(dane, 0, tacert, depth, WRAP_MID))
+        return grow_chain(dane, UNTRUSTED, tacert);
+    return 0;
+}
+
+static int ta_signed(SSL_DANE *dane, X509 *cert, int depth)
+{
+    DANE_CERT_LIST x;
+    DANE_PKEY_LIST k;
+    EVP_PKEY *pk;
+    int done = 0;
+
+    /*
+     * First check whether issued and signed by a TA cert, this is cheaper
+     * than the bare-public key checks below, since we can determine whether
+     * the candidate TA certificate issued the certificate to be checked
+     * first (name comparisons), before we bother with signature checks
+     * (public key operations).
+     */
+    for (x = dane->certs; !done && x; x = x->next) {
+        if (X509_check_issued(x->value, cert) == X509_V_OK) {
+            if ((pk = X509_get_pubkey(x->value)) == 0) {
+                /*
+                 * The cert originally contained a valid pkey, which does
+                 * not just vanish, so this is most likely a memory error.
+                 */
+                done = -1;
+                break;
+            }
+            /* Check signature, since some other TA may work if not this. */
+            if (X509_verify(cert, pk) > 0)
+                done = wrap_cert(dane, x->value, depth) ? 1 : -1;
+            EVP_PKEY_free(pk);
+        }
+    }
+
+    /*
+     * With bare TA public keys, we can't check whether the trust chain is
+     * issued by the key, but we can determine whether it is signed by the
+     * key, so we go with that.
+     *
+     * Ideally, the corresponding certificate was presented in the chain, and we
+     * matched it by its public key digest one level up.  This code is here
+     * to handle adverse conditions imposed by sloppy administrators of
+     * receiving systems with poorly constructed chains.
+     *
+     * We'd like to optimize out keys that should not match when the cert's
+     * authority key id does not match the key id of this key computed via
+     * the RFC keyid algorithm (SHA-1 digest of public key bit-string sans
+     * ASN1 tag and length thus also excluding the unused bits field that is
+     * logically part of the length).  However, some CAs have a non-standard
+     * authority keyid, so we lose.  Too bad.
+     *
+     * This may push errors onto the stack when the certificate signature is
+     * not of the right type or length, throw these away,
+     */
+    for (k = dane->pkeys; !done && k; k = k->next)
+        if (X509_verify(cert, k->value) > 0)
+            done = wrap_issuer(dane, k->value, cert, depth, WRAP_MID) ? 1 : -1;
+        else
+            ERR_clear_error();
+
+    return done;
+}
+
+static int set_trust_anchor(X509_STORE_CTX *ctx, SSL_DANE *dane, X509 *cert)
+{
+    int matched = 0;
+    int n;
+    int i;
+    int depth = 0;
+    EVP_PKEY *takey;
+    X509 *ca;
+    STACK_OF(X509) *in = ctx->untrusted;        /* XXX: Accessor? */
+
+    if (!grow_chain(dane, UNTRUSTED, 0))
+        return -1;
+
+    /*
+     * Accept a degenerate case: depth 0 self-signed trust-anchor.
+     */
+    if (X509_check_issued(cert, cert) == X509_V_OK) {
+        dane->depth = 0;
+        matched = match(dane->selectors[SSL_DANE_USAGE_TRUSTED_CA], cert, 0);
+        if (matched > 0 && !grow_chain(dane, TRUSTED, cert))
+            matched = -1;
+        return matched;
+    }
+
+    /* Make a shallow copy of the input untrusted chain. */
+    if ((in = sk_X509_dup(in)) == 0) {
+        DANEerr(DANE_F_SET_TRUST_ANCHOR, ERR_R_MALLOC_FAILURE);
+        return -1;
+    }
+
+    /*
+     * At each iteration we consume the issuer of the current cert.  This
+     * reduces the length of the "in" chain by one.  If no issuer is found,
+     * we are done.  We also stop when a certificate matches a TA in the
+     * peer's TLSA RRset.
+     *
+     * Caller ensures that the initial certificate is not self-signed.
+     */
+    for (n = sk_X509_num(in); n > 0; --n, ++depth) {
+        for (i = 0; i < n; ++i)
+            if (X509_check_issued(sk_X509_value(in, i), cert) == X509_V_OK)
+                break;
+
+        /*
+         * Final untrusted element with no issuer in the peer's chain, it may
+         * however be signed by a pkey or cert obtained via a TLSA RR.
+         */
+        if (i == n)
+            break;
+
+        /* Peer's chain contains an issuer ca. */
+        ca = sk_X509_delete(in, i);
+
+        /* If not a trust anchor, record untrusted ca and continue. */
+        if ((matched = match(dane->selectors[SSL_DANE_USAGE_TRUSTED_CA], ca,
+                             depth + 1)) == 0) {
+            if (grow_chain(dane, UNTRUSTED, ca)) {
+                if (!X509_check_issued(ca, ca) == X509_V_OK) {
+                    /* Restart with issuer as subject */
+                    cert = ca;
+                    continue;
+                }
+                /* Final self-signed element, skip ta_signed() check. */
+                cert = 0;
+            } else
+                matched = -1;
+        } else if (matched == MATCHED_CERT) {
+            if (!wrap_cert(dane, ca, depth))
+                matched = -1;
+        } else if (matched == MATCHED_PKEY) {
+            if ((takey = X509_get_pubkey(ca)) == 0 ||
+                !wrap_issuer(dane, takey, cert, depth, WRAP_MID)) {
+                if (takey)
+                    EVP_PKEY_free(takey);
+                else
+                    DANEerr(DANE_F_SET_TRUST_ANCHOR, ERR_R_MALLOC_FAILURE);
+                matched = -1;
+            }
+        }
+        break;
+    }
+
+    /* Shallow free the duplicated input untrusted chain. */
+    sk_X509_free(in);
+
+    /*
+     * When the loop exits, if "cert" is set, it is not self-signed and has
+     * no issuer in the chain, we check for a possible signature via a DNS
+     * obtained TA cert or public key.
+     */
+    if (matched == 0 && cert)
+         matched = ta_signed(dane, cert, depth);
+
+    return matched;
+}
+
+static int check_end_entity(X509_STORE_CTX *ctx, SSL_DANE *dane, X509 *cert)
+{
+    int matched;
+
+    matched = match(dane->selectors[SSL_DANE_USAGE_FIXED_LEAF], cert, 0);
+    if (matched > 0) {
+        if (ctx->chain == 0) {
+            if ((ctx->chain = sk_X509_new_null()) != 0 &&
+                sk_X509_push(ctx->chain, cert)) {
+                CRYPTO_add(&cert->references, 1, CRYPTO_LOCK_X509);
+            } else {
+                DANEerr(DANE_F_CHECK_END_ENTITY, ERR_R_MALLOC_FAILURE);
+                return -1;
+            }
+        }
+    }
+    return matched;
+}
+
+static int match_name(const char *certid, SSL_DANE *dane)
+{
+    int multi = dane->multi;
+    DANE_HOST_LIST hosts = dane->hosts;
+
+    for (/* NOP */; hosts; hosts = hosts->next) {
+        int match_subdomain = 0;
+        const char *domain = hosts->value;
+        const char *parent;
+        int idlen;
+        int domlen;
+
+        if (*domain == '.' && domain[1] != '\0') {
+            ++domain;
+            match_subdomain = 1;
+        }
+
+        /*
+         * Sub-domain match: certid is any sub-domain of hostname.
+         */
+        if (match_subdomain) {
+            if ((idlen = strlen(certid)) > (domlen = strlen(domain)) + 1
+                && certid[idlen - domlen - 1] == '.'
+                && !strcasecmp(certid + (idlen - domlen), domain))
+                return 1;
+            else
+                continue;
+        }
+
+        /*
+         * Exact match and initial "*" match. The initial "*" in a certid
+         * matches one (if multi is false) or more hostname components under
+         * the condition that the certid contains multiple hostname components.
+         */
+        if (!strcasecmp(certid, domain)
+            || (certid[0] == '*' && certid[1] == '.' && certid[2] != 0
+                && (parent = strchr(domain, '.')) != 0
+                && (idlen = strlen(certid + 1)) <= (domlen = strlen(parent))
+                && strcasecmp(multi ? parent + domlen - idlen : parent,
+                              certid + 1) == 0))
+            return 1;
+    }
+    return 0;
+}
+
+static char *check_name(char *name, int len)
+{
+    register char *cp = name + len;
+
+    while (len > 0 && *--cp == 0)
+        --len;                          /* Ignore trailing NULs */
+    if (len <= 0)
+        return 0;
+    for (cp = name; *cp; cp++) {
+        register char c = *cp;
+        if (!((c >= 'a' && c <= 'z') ||
+              (c >= '0' && c <= '9') ||
+              (c >= 'A' && c <= 'Z') ||
+              (c == '.' || c == '-') ||
+              (c == '*')))
+            return 0;                   /* Only LDH, '.' and '*' */
+    }
+    if (cp - name != len)               /* Guard against internal NULs */
+        return 0;
+    return name;
+}
+
+static char *parse_dns_name(const GENERAL_NAME *gn)
+{
+    if (gn->type != GEN_DNS)
+        return 0;
+    if (ASN1_STRING_type(gn->d.ia5) != V_ASN1_IA5STRING)
+        return 0;
+    return check_name((char *) ASN1_STRING_data(gn->d.ia5),
+                      ASN1_STRING_length(gn->d.ia5));
+}
+
+static char *parse_subject_name(X509 *cert)
+{
+    X509_NAME *name = X509_get_subject_name(cert);
+    X509_NAME_ENTRY *entry;
+    ASN1_STRING *entry_str;
+    unsigned char *namebuf;
+    int nid = NID_commonName;
+    int len;
+    int i;
+
+    if (name == 0 || (i = X509_NAME_get_index_by_NID(name, nid, -1)) < 0)
+        return 0;
+    if ((entry = X509_NAME_get_entry(name, i)) == 0)
+        return 0;
+    if ((entry_str = X509_NAME_ENTRY_get_data(entry)) == 0)
+        return 0;
+
+    if ((len = ASN1_STRING_to_UTF8(&namebuf, entry_str)) < 0)
+        return 0;
+    if (len <= 0 || check_name((char *) namebuf, len) == 0) {
+        OPENSSL_free(namebuf);
+        return 0;
+    }
+    return (char *) namebuf;
+}
+
+static int name_check(SSL_DANE *dane, X509 *cert)
+{
+    int matched = 0;
+    int got_altname = 0;
+    GENERAL_NAMES *gens;
+
+    gens = X509_get_ext_d2i(cert, NID_subject_alt_name, 0, 0);
+    if (gens) {
+        int n = sk_GENERAL_NAME_num(gens);
+        int i;
+
+        for (i = 0; i < n; ++i) {
+            const GENERAL_NAME *gn = sk_GENERAL_NAME_value(gens, i);
+            const char *certid;
+
+            if (gn->type != GEN_DNS)
+                continue;
+            got_altname = 1;
+            certid = parse_dns_name(gn);
+            if (certid && *certid) {
+                if ((matched = match_name(certid, dane)) == 0)
+                    continue;
+                if ((dane->mhost = OPENSSL_strdup(certid)) == 0)
+                    matched = -1;
+                break;
+            }
+        }
+        GENERAL_NAMES_free(gens);
+    }
+
+    /*
+     * XXX: Should the subjectName be skipped when *any* altnames are present,
+     * or only when DNS altnames are present?
+     */
+    if (got_altname == 0) {
+        char *certid = parse_subject_name(cert);
+        if (certid != 0 && *certid && (matched = match_name(certid, dane)) != 0)
+            dane->mhost = certid;       /* Already a copy */
+    }
+    return matched;
+}
+
+static int verify_chain(X509_STORE_CTX *ctx)
+{
+    DANE_SELECTOR_LIST issuer_rrs;
+    DANE_SELECTOR_LIST leaf_rrs;
+    int (*cb)(int, X509_STORE_CTX *) = ctx->verify_cb;
+    int ssl_idx = SSL_get_ex_data_X509_STORE_CTX_idx();
+    SSL *ssl = X509_STORE_CTX_get_ex_data(ctx, ssl_idx);
+    SSL_DANE *dane = SSL_get_ex_data(ssl, dane_idx);
+    X509 *cert = ctx->cert;             /* XXX: accessor? */
+    int matched = 0;
+    int chain_length = sk_X509_num(ctx->chain);
+
+    issuer_rrs = dane->selectors[SSL_DANE_USAGE_LIMIT_ISSUER];
+    leaf_rrs = dane->selectors[SSL_DANE_USAGE_LIMIT_LEAF];
+    ctx->verify = dane->verify;
+
+    if ((matched = name_check(dane, cert)) < 0) {
+        X509_STORE_CTX_set_error(ctx, X509_V_ERR_OUT_OF_MEM);
+        return 0;
+    }
+
+    if (!matched) {
+        ctx->error_depth = 0;
+        ctx->current_cert = cert;
+        X509_STORE_CTX_set_error(ctx, X509_V_ERR_HOSTNAME_MISMATCH);
+        if (!cb(0, ctx))
+            return 0;
+    }
+    matched = 0;
+
+    /*
+     * Satisfy at least one usage 0 or 1 constraint, unless we've already
+     * matched a usage 2 trust anchor.
+     *
+     * XXX: internal_verify() doesn't callback with top certs that are not
+     * self-issued.  This should be fixed in a future OpenSSL.
+     */
+    if (dane->roots && sk_X509_num(dane->roots)) {
+#ifndef NO_CALLBACK_WORKAROUND
+        X509 *top = sk_X509_value(ctx->chain, dane->depth);
+
+        if (X509_check_issued(top, top) != X509_V_OK) {
+            ctx->error_depth = dane->depth;
+            ctx->current_cert = top;
+            if (!cb(1, ctx))
+                return 0;
+        }
+#endif
+        /* Pop synthetic trust-anchor ancestors off the chain! */
+        while (--chain_length > dane->depth)
+            X509_free(sk_X509_pop(ctx->chain));
+    } else if (issuer_rrs || leaf_rrs) {
+        int n = chain_length;
+
+        /*
+         * Check for an EE match, then a CA match at depths > 0, and
+         * finally, if the EE cert is self-issued, for a depth 0 CA match.
+         */
+        if (leaf_rrs)
+            matched = match(leaf_rrs, cert, 0);
+        while (!matched && issuer_rrs && --n >= 0) {
+            X509 *xn = sk_X509_value(ctx->chain, n);
+
+            if (n > 0 || X509_check_issued(xn, xn) == X509_V_OK)
+                matched = match(issuer_rrs, xn, n);
+        }
+
+        if (matched < 0) {
+            X509_STORE_CTX_set_error(ctx, X509_V_ERR_OUT_OF_MEM);
+            return 0;
+        }
+
+        if (!matched) {
+            ctx->current_cert = cert;
+            ctx->error_depth = 0;
+            X509_STORE_CTX_set_error(ctx, X509_V_ERR_CERT_UNTRUSTED);
+            if (!cb(0, ctx))
+                return 0;
+        }
+    }
+
+    return ctx->verify(ctx);
+}
+
+static int verify_cert(X509_STORE_CTX *ctx, void *unused_ctx)
+{
+    static int ssl_idx = -1;
+    SSL *ssl;
+    SSL_DANE *dane;
+    int (*cb)(int, X509_STORE_CTX *) = ctx->verify_cb;
+    int matched;
+    X509 *cert = ctx->cert;             /* XXX: accessor? */
+
+    if (ssl_idx < 0)
+        ssl_idx = SSL_get_ex_data_X509_STORE_CTX_idx();
+    if (dane_idx < 0) {
+        DANEerr(DANE_F_VERIFY_CERT, ERR_R_MALLOC_FAILURE);
+        return -1;
+    }
+
+    ssl = X509_STORE_CTX_get_ex_data(ctx, ssl_idx);
+    if ((dane = SSL_get_ex_data(ssl, dane_idx)) == 0 || cert == 0)
+        return X509_verify_cert(ctx);
+
+    if (dane->selectors[SSL_DANE_USAGE_FIXED_LEAF]) {
+        if ((matched = check_end_entity(ctx, dane, cert)) > 0) {
+            ctx->error_depth = 0;
+            ctx->current_cert = cert;
+            return cb(1, ctx);
+        }
+        if (matched < 0) {
+            X509_STORE_CTX_set_error(ctx, X509_V_ERR_OUT_OF_MEM);
+            return -1;
+        }
+    }
+
+    if (dane->selectors[SSL_DANE_USAGE_TRUSTED_CA]) {
+        if ((matched = set_trust_anchor(ctx, dane, cert)) < 0) {
+            X509_STORE_CTX_set_error(ctx, X509_V_ERR_OUT_OF_MEM);
+            return -1;
+        }
+        if (matched) {
+            /*
+             * Check that setting the untrusted chain updates the expected
+             * structure member at the expected offset.
+             */
+            X509_STORE_CTX_trusted_stack(ctx, dane->roots);
+            X509_STORE_CTX_set_chain(ctx, dane->chain);
+            OPENSSL_assert(ctx->untrusted == dane->chain);
+        }
+    }
+
+    /*
+     * Name checks and usage 0/1 constraint enforcement are delayed until
+     * X509_verify_cert() builds the full chain and calls our verify_chain()
+     * wrapper.
+     */
+    dane->verify = ctx->verify;
+    ctx->verify = verify_chain;
+
+    return X509_verify_cert(ctx);
+}
+
+static dane_list list_alloc(size_t vsize)
+{
+    void *value = (void *) OPENSSL_malloc(vsize);
+    dane_list l;
+
+    if (value == 0) {
+        DANEerr(DANE_F_LIST_ALLOC, ERR_R_MALLOC_FAILURE);
+        return 0;
+    }
+    if ((l = (dane_list) OPENSSL_malloc(sizeof(*l))) == 0) {
+        OPENSSL_free(value);
+        DANEerr(DANE_F_LIST_ALLOC, ERR_R_MALLOC_FAILURE);
+        return 0;
+    }
+    l->next = 0;
+    l->value = value;
+    return l;
+}
+
+static void list_free(void *list, void (*f)(void *))
+{
+    dane_list head = (dane_list) list;
+    dane_list next;
+
+    for (/* NOP */; head; head = next) {
+        next = head->next;
+        if (f && head->value)
+            f(head->value);
+        OPENSSL_free(head);
+    }
+}
+
+static void dane_mtype_free(void *p)
+{
+    list_free(((dane_mtype) p)->data, OPENSSL_freeFunc);
+    OPENSSL_free(p);
+}
+
+static void dane_selector_free(void *p)
+{
+    list_free(((dane_selector) p)->mtype, dane_mtype_free);
+    OPENSSL_free(p);
+}
+
+void DANESSL_cleanup(SSL *ssl)
+{
+    SSL_DANE *dane;
+    int u;
+
+    if (dane_idx < 0 || (dane = SSL_get_ex_data(ssl, dane_idx)) == 0)
+        return;
+    (void) SSL_set_ex_data(ssl, dane_idx, 0);
+
+    if (dane->hosts)
+        list_free(dane->hosts, OPENSSL_freeFunc);
+    if (dane->mhost)
+        OPENSSL_free(dane->mhost);
+    for (u = 0; u <= SSL_DANE_USAGE_LAST; ++u)
+        if (dane->selectors[u])
+            list_free(dane->selectors[u], dane_selector_free);
+    if (dane->pkeys)
+        list_free(dane->pkeys, pkey_free);
+    if (dane->certs)
+        list_free(dane->certs, cert_free);
+    if (dane->roots)
+        sk_X509_pop_free(dane->roots, X509_free);
+    if (dane->chain)
+        sk_X509_pop_free(dane->chain, X509_free);
+    OPENSSL_free(dane);
+}
+
+static DANE_HOST_LIST host_list_init(const char **src)
+{
+    DANE_HOST_LIST head = 0;
+
+    while (*src) {
+        DANE_HOST_LIST elem = (DANE_HOST_LIST) OPENSSL_malloc(sizeof(*elem));
+        if (elem == 0) {
+            list_free(head, OPENSSL_freeFunc);
+            return 0;
+        }
+        elem->value = OPENSSL_strdup(*src++);
+        LINSERT(head, elem);
+    }
+    return head;
+}
+
+int DANESSL_add_tlsa(
+        SSL *ssl,
+        uint8_t usage,
+        uint8_t selector,
+        const char *mdname,
+        unsigned const char *data,
+        size_t dlen
+)
+{
+    SSL_DANE *dane;
+    DANE_SELECTOR_LIST s = 0;
+    DANE_MTYPE_LIST m = 0;
+    DANE_DATA_LIST d = 0;
+    DANE_CERT_LIST xlist = 0;
+    DANE_PKEY_LIST klist = 0;
+    const EVP_MD *md = 0;
+
+    if (dane_idx < 0 || (dane = SSL_get_ex_data(ssl, dane_idx)) == 0) {
+        DANEerr(DANE_F_SSL_DANE_ADD_TLSA, DANE_R_DANE_INIT);
+        return -1;
+    }
+
+    if (usage > SSL_DANE_USAGE_LAST) {
+        DANEerr(DANE_F_SSL_DANE_ADD_TLSA, DANE_R_BAD_USAGE);
+        return 0;
+    }
+    if (selector > SSL_DANE_SELECTOR_LAST) {
+        DANEerr(DANE_F_SSL_DANE_ADD_TLSA, DANE_R_BAD_SELECTOR);
+        return 0;
+    }
+    if (mdname && (md = EVP_get_digestbyname(mdname)) == 0) {
+        DANEerr(DANE_F_SSL_DANE_ADD_TLSA, DANE_R_BAD_DIGEST);
+        return 0;
+    }
+    if (!data) {
+        DANEerr(DANE_F_SSL_DANE_ADD_TLSA, DANE_R_BAD_NULL_DATA);
+        return 0;
+    }
+    if (mdname && dlen != EVP_MD_size(md)) {
+        DANEerr(DANE_F_SSL_DANE_ADD_TLSA, DANE_R_BAD_DATA_LENGTH);
+        return 0;
+    }
+
+    if (mdname == 0) {
+        X509 *x = 0;
+        EVP_PKEY *k = 0;
+        const unsigned char *p = data;
+
+#define xklistinit(lvar, ltype, var, freeFunc) do { \
+            (lvar) = (ltype) OPENSSL_malloc(sizeof(*(lvar))); \
+            if ((lvar) == 0) { \
+                DANEerr(DANE_F_SSL_DANE_ADD_TLSA, ERR_R_MALLOC_FAILURE); \
+                freeFunc((var)); \
+                return 0; \
+            } \
+            (lvar)->next = 0; \
+            lvar->value = var; \
+        } while (0)
+#define xkfreeret(ret) do { \
+            if (xlist) list_free(xlist, cert_free); \
+            if (klist) list_free(klist, pkey_free); \
+            return (ret); \
+        } while (0)
+
+        switch (selector) {
+        case SSL_DANE_SELECTOR_CERT:
+            if (!d2i_X509(&x, &p, dlen) || dlen != p - data) {
+                if (x)
+                    X509_free(x);
+                DANEerr(DANE_F_SSL_DANE_ADD_TLSA, DANE_R_BAD_CERT);
+                return 0;
+            }
+            k = X509_get_pubkey(x);
+            EVP_PKEY_free(k);
+            if (k == 0) {
+                X509_free(x);
+                DANEerr(DANE_F_SSL_DANE_ADD_TLSA, DANE_R_BAD_CERT_PKEY);
+                return 0;
+            }
+            if (usage == SSL_DANE_USAGE_TRUSTED_CA)
+                xklistinit(xlist, DANE_CERT_LIST, x, X509_free);
+            break;
+
+        case SSL_DANE_SELECTOR_SPKI:
+            if (!d2i_PUBKEY(&k, &p, dlen) || dlen != p - data) {
+                if (k)
+                    EVP_PKEY_free(k);
+                DANEerr(DANE_F_SSL_DANE_ADD_TLSA, DANE_R_BAD_PKEY);
+                return 0;
+            }
+            if (usage == SSL_DANE_USAGE_TRUSTED_CA)
+                xklistinit(klist, DANE_PKEY_LIST, k, EVP_PKEY_free);
+            break;
+        }
+    }
+
+    /* Find insertion point and don't add duplicate elements. */
+    for (s = dane->selectors[usage]; s; s = s->next)
+        if (s->value->selector == selector)
+            for (m = s->value->mtype; m; m = m->next)
+                if (m->value->md == md)
+                    for (d = m->value->data; d; d = d->next)
+                        if (d->value->datalen == dlen &&
+                            memcmp(d->value->data, data, dlen) == 0)
+                            xkfreeret(1);
+
+    if ((d = (DANE_DATA_LIST) list_alloc(sizeof(*d->value) + dlen)) == 0)
+        xkfreeret(0);
+    d->value->datalen = dlen;
+    memcpy(d->value->data, data, dlen);
+    if (!m) {
+        if ((m = (DANE_MTYPE_LIST) list_alloc(sizeof(*m->value))) == 0) {
+            list_free(d, OPENSSL_freeFunc);
+            xkfreeret(0);
+        }
+        m->value->data = 0;
+        if ((m->value->md = md) != 0)
+            m->value->mdlen = dlen;
+        if (!s) {
+            if ((s = (DANE_SELECTOR_LIST) list_alloc(sizeof(*s->value))) == 0) {
+                list_free(m, dane_mtype_free);
+                xkfreeret(0);
+            }
+            s->value->mtype = 0;
+            s->value->selector = selector;
+            LINSERT(dane->selectors[usage], s);
+        }
+        LINSERT(s->value->mtype, m);
+    }
+    LINSERT(m->value->data, d);
+
+    if (xlist)
+        LINSERT(dane->certs, xlist);
+    else if (klist)
+        LINSERT(dane->pkeys, klist);
+    ++dane->count;
+    return 1;
+}
+
+int DANESSL_init(SSL *ssl, const char *sni_domain, const char **hostnames)
+{
+    SSL_DANE *dane;
+    int i;
+#ifdef OPENSSL_INTERNAL
+    SSL_CTX *sctx = SSL_get_SSL_CTX(ssl);
+
+    if (sctx->app_verify_callback != verify_cert) {
+        DANEerr(DANE_F_SSL_DANE_INIT, DANE_R_SCTX_INIT);
+        return -1;
+    }
+#else
+    if (dane_idx < 0) {
+        DANEerr(DANE_F_SSL_DANE_INIT, DANE_R_LIBRARY_INIT);
+        return -1;
+    }
+#endif
+
+    if (sni_domain && !SSL_set_tlsext_host_name(ssl, sni_domain))
+        return 0;
+
+    if ((dane = (SSL_DANE *) OPENSSL_malloc(sizeof(SSL_DANE))) == 0) {
+        DANEerr(DANE_F_SSL_DANE_INIT, ERR_R_MALLOC_FAILURE);
+        return 0;
+    }
+    if (!SSL_set_ex_data(ssl, dane_idx, dane)) {
+        DANEerr(DANE_F_SSL_DANE_INIT, ERR_R_MALLOC_FAILURE);
+        OPENSSL_free(dane);
+        return 0;
+    }
+
+    dane->pkeys = 0;
+    dane->certs = 0;
+    dane->chain = 0;
+    dane->roots = 0;
+    dane->depth = -1;
+    dane->mhost = 0;                    /* Future SSL control interface */
+    dane->multi = 0;                    /* Future SSL control interface */
+    dane->count = 0;
+
+    for (i = 0; i <= SSL_DANE_USAGE_LAST; ++i)
+        dane->selectors[i] = 0;
+
+    if (hostnames && (dane->hosts = host_list_init(hostnames)) == 0) {
+        DANEerr(DANE_F_SSL_DANE_INIT, ERR_R_MALLOC_FAILURE);
+        DANESSL_cleanup(ssl);
+        return 0;
+    }
+
+    return 1;
+}
+
+int DANESSL_CTX_init(SSL_CTX *ctx)
+{
+    if (dane_idx >= 0) {
+        SSL_CTX_set_cert_verify_callback(ctx, verify_cert, 0);
+        return 1;
+    }
+    DANEerr(DANE_F_SSL_CTX_DANE_INIT, DANE_R_LIBRARY_INIT);
+    return -1;
+}
+
+static int init_once(
+        volatile int *value,
+        int (*init)(void),
+        void (*postinit)(void)
+)
+{
+    int wlock = 0;
+
+    CRYPTO_r_lock(CRYPTO_LOCK_SSL_CTX);
+    if (*value < 0) {
+        CRYPTO_r_unlock(CRYPTO_LOCK_SSL_CTX);
+        CRYPTO_w_lock(CRYPTO_LOCK_SSL_CTX);
+        wlock = 1;
+        if (*value < 0) {
+            *value = init();
+            if (postinit)
+                postinit();
+        }
+    }
+    if (wlock)
+        CRYPTO_w_unlock(CRYPTO_LOCK_SSL_CTX);
+    else
+        CRYPTO_r_unlock(CRYPTO_LOCK_SSL_CTX);
+    return *value;
+}
+
+static void dane_init(void)
+{
+    /*
+     * Store library id in zeroth function slot, used to locate the library
+     * name.  This must be done before we load the error strings.
+     */
+#ifndef OPENSSL_NO_ERR
+    dane_str_functs[0].error |= ERR_PACK(err_lib_dane, 0, 0);
+    ERR_load_strings(err_lib_dane, dane_str_functs);
+    ERR_load_strings(err_lib_dane, dane_str_reasons);
+#endif
+
+    /*
+     * Register SHA-2 digests, if implemented and not already registered.
+     */
+#if defined(LN_sha256) && defined(NID_sha256) && !defined(OPENSSL_NO_SHA256)
+    if (!EVP_get_digestbyname(LN_sha224))
+        EVP_add_digest(EVP_sha224());
+    if (!EVP_get_digestbyname(LN_sha256))
+        EVP_add_digest(EVP_sha256());
+#endif
+#if defined(LN_sha512) && defined(NID_sha512) && !defined(OPENSSL_NO_SHA512)
+    if (!EVP_get_digestbyname(LN_sha384))
+        EVP_add_digest(EVP_sha384());
+    if (!EVP_get_digestbyname(LN_sha512))
+        EVP_add_digest(EVP_sha512());
+#endif
+
+    /*
+     * Register an SSL index for the connection-specific SSL_DANE structure.
+     * Using a separate index makes it possible to add DANE support to
+     * existing OpenSSL releases that don't have a suitable pointer in the
+     * SSL structure.
+     */
+    dane_idx = SSL_get_ex_new_index(0, 0, 0, 0, 0);
+}
+
+int DANESSL_library_init(void)
+{
+    if (err_lib_dane < 0)
+        init_once(&err_lib_dane, ERR_get_next_error_library, dane_init);
+
+#if defined(LN_sha256)
+    /* No DANE without SHA256 support */
+    if (dane_idx >= 0 && EVP_get_digestbyname(LN_sha256) != 0)
+        return 1;
+#endif
+    DANEerr(DANE_F_SSL_DANE_LIBRARY_INIT, DANE_R_DANE_SUPPORT);
+    return 0;
+}
+
+#endif /* OPENSSL_VERSION_NUMBER */
diff --git a/src/src/dane.c b/src/src/dane.c
new file mode 100644
index 000000000..54fd00cee
--- /dev/null
+++ b/src/src/dane.c
@@ -0,0 +1,46 @@
+/*************************************************
+*     Exim - an Internet mail transport agent    *
+*************************************************/
+
+/* Copyright (c) University of Cambridge 1995 - 2012 */
+/* See the file NOTICE for conditions of use and distribution. */
+
+/* This module provides TLS (aka SSL) support for Exim. The code for OpenSSL is
+based on a patch that was originally contributed by Steve Haslam. It was
+adapted from stunnel, a GPL program by Michal Trojnara. The code for GNU TLS is
+based on a patch contributed by Nikos Mavroyanopoulos. Because these packages
+are so very different, the functions for each are kept in separate files. The
+relevant file is #included as required, after any any common functions.
+
+No cryptographic code is included in Exim. All this module does is to call
+functions from the OpenSSL or GNU TLS libraries. */
+
+
+#include "exim.h"
+
+/* This module is compiled only when it is specifically requested in the
+build-time configuration. However, some compilers don't like compiling empty
+modules, so keep them happy with a dummy when skipping the rest. Make it
+reference itself to stop picky compilers complaining that it is unused, and put
+in a dummy argument to stop even pickier compilers complaining about infinite
+loops. */
+
+#ifndef EXPERIMENTAL_DANE
+static void dummy(int x) { dummy(x-1); }
+#else
+
+/* Enabling DANE without enabling TLS cannot work. Abort the compilation. */
+#ifndef SUPPORT_TLS
+#error DANE support requires that TLS support must be enabled. Abort build.
+#endif
+
+#ifdef USE_GNUTLS
+#include "dane-gnu.c"
+#else
+#include "dane-openssl.c"
+#endif
+
+
+#endif  /* EXPERIMENTAL_DANE */
+
+/* End of dane.c */
diff --git a/src/src/danessl.h b/src/src/danessl.h
new file mode 100644
index 000000000..5b1584da2
--- /dev/null
+++ b/src/src/danessl.h
@@ -0,0 +1,31 @@
+#ifndef HEADER_SSL_DANE_H
+#define HEADER_SSL_DANE_H
+
+#include <stdint.h>
+#include <openssl/ssl.h>
+
+/*-
+ * Certificate usages:
+ * https://tools.ietf.org/html/rfc6698#section-2.1.1
+ */
+#define SSL_DANE_USAGE_LIMIT_ISSUER     0
+#define SSL_DANE_USAGE_LIMIT_LEAF       1
+#define SSL_DANE_USAGE_TRUSTED_CA       2
+#define SSL_DANE_USAGE_FIXED_LEAF       3
+#define SSL_DANE_USAGE_LAST             SSL_DANE_USAGE_FIXED_LEAF
+
+/*-
+ * Selectors:
+ * https://tools.ietf.org/html/rfc6698#section-2.1.2
+ */
+#define SSL_DANE_SELECTOR_CERT          0
+#define SSL_DANE_SELECTOR_SPKI          1
+#define SSL_DANE_SELECTOR_LAST          SSL_DANE_SELECTOR_SPKI
+
+extern int DANESSL_library_init(void);
+extern int DANESSL_CTX_init(SSL_CTX *);
+extern int DANESSL_init(SSL *, const char *, const char **);
+extern void DANESSL_cleanup(SSL *);
+extern int DANESSL_add_tlsa(SSL *, uint8_t, uint8_t, const char *,
+                            unsigned const char *, size_t);
+#endif
diff --git a/src/src/globals.c b/src/src/globals.c
index d3f99877c..7d4ab63a1 100644
--- a/src/src/globals.c
+++ b/src/src/globals.c
@@ -633,6 +633,9 @@ BOOL    dmarc_enable_forensic   = FALSE;
 uschar *dns_again_means_nonexist = NULL;
 int     dns_csa_search_limit   = 5;
 BOOL    dns_csa_use_reverse    = TRUE;
+#ifdef EXPERIMENTAL_DANE
+int     dns_dane_ok            = -1;
+#endif
 uschar *dns_ipv4_lookup        = NULL;
 int     dns_retrans            = 0;
 int     dns_retry              = 0;
diff --git a/src/src/globals.h b/src/src/globals.h
index 2bedcf523..32ddd16e2 100644
--- a/src/src/globals.h
+++ b/src/src/globals.h
@@ -385,6 +385,9 @@ extern uschar *dns_again_means_nonexist; /* Domains that are badly set up */
 extern int     dns_csa_search_limit;   /* How deep to search for CSA SRV records */
 extern BOOL    dns_csa_use_reverse;    /* Check CSA in reverse DNS? (non-standard) */
 extern uschar *dns_ipv4_lookup;        /* For these domains, don't look for AAAA (or A6) */
+#ifdef EXPERIMENTAL_DANE
+extern int     dns_dane_ok;            /* Ok to use DANE when checking TLS authenticity */
+#endif
 extern int     dns_retrans;            /* Retransmission time setting */
 extern int     dns_retry;              /* Number of retries */
 extern int     dns_dnssec_ok;          /* When constructing DNS query, set DO flag */