diff --git a/ssl/ssl_versions.c b/ssl/ssl_versions.c
new file mode 100644
index 0000000..6565688
--- /dev/null
+++ b/ssl/ssl_versions.c
@@ -0,0 +1,326 @@
+/* Copyright (c) 2017, Google Inc.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
+
+#include <openssl/ssl.h>
+
+#include <assert.h>
+
+#include <openssl/bytestring.h>
+#include <openssl/err.h>
+
+#include "internal.h"
+#include "../crypto/internal.h"
+
+
+int ssl_protocol_version_from_wire(uint16_t *out, uint16_t version) {
+  switch (version) {
+    case SSL3_VERSION:
+    case TLS1_VERSION:
+    case TLS1_1_VERSION:
+    case TLS1_2_VERSION:
+      *out = version;
+      return 1;
+
+    case TLS1_3_DRAFT_VERSION:
+      *out = TLS1_3_VERSION;
+      return 1;
+
+    case DTLS1_VERSION:
+      /* DTLS 1.0 is analogous to TLS 1.1, not TLS 1.0. */
+      *out = TLS1_1_VERSION;
+      return 1;
+
+    case DTLS1_2_VERSION:
+      *out = TLS1_2_VERSION;
+      return 1;
+
+    default:
+      return 0;
+  }
+}
+
+/* The follow arrays are the supported versions for TLS and DTLS, in order of
+ * decreasing preference. */
+
+static const uint16_t kTLSVersions[] = {
+    TLS1_3_DRAFT_VERSION,
+    TLS1_2_VERSION,
+    TLS1_1_VERSION,
+    TLS1_VERSION,
+    SSL3_VERSION,
+};
+
+static const uint16_t kDTLSVersions[] = {
+    DTLS1_2_VERSION,
+    DTLS1_VERSION,
+};
+
+static void get_method_versions(const SSL_PROTOCOL_METHOD *method,
+                                const uint16_t **out, size_t *out_num) {
+  if (method->is_dtls) {
+    *out = kDTLSVersions;
+    *out_num = OPENSSL_ARRAY_SIZE(kDTLSVersions);
+  } else {
+    *out = kTLSVersions;
+    *out_num = OPENSSL_ARRAY_SIZE(kTLSVersions);
+  }
+}
+
+static int method_supports_version(const SSL_PROTOCOL_METHOD *method,
+                                   uint16_t version) {
+  const uint16_t *versions;
+  size_t num_versions;
+  get_method_versions(method, &versions, &num_versions);
+  for (size_t i = 0; i < num_versions; i++) {
+    if (versions[i] == version) {
+      return 1;
+    }
+  }
+  return 0;
+}
+
+static int set_version_bound(const SSL_PROTOCOL_METHOD *method, uint16_t *out,
+                             uint16_t version) {
+  /* The public API uses wire versions, except we use |TLS1_3_VERSION|
+   * everywhere to refer to any draft TLS 1.3 versions. In this direction, we
+   * map it to some representative TLS 1.3 draft version. */
+  if (version == TLS1_3_VERSION) {
+    version = TLS1_3_DRAFT_VERSION;
+  }
+
+  return method_supports_version(method, version) &&
+         ssl_protocol_version_from_wire(out, version);
+}
+
+static int set_min_version(const SSL_PROTOCOL_METHOD *method, uint16_t *out,
+                           uint16_t version) {
+  /* Zero is interpreted as the default minimum version. */
+  if (version == 0) {
+    /* SSL 3.0 is disabled by default and TLS 1.0 does not exist in DTLS. */
+    *out = method->is_dtls ? TLS1_1_VERSION : TLS1_VERSION;
+    return 1;
+  }
+
+  return set_version_bound(method, out, version);
+}
+
+static int set_max_version(const SSL_PROTOCOL_METHOD *method, uint16_t *out,
+                           uint16_t version) {
+  /* Zero is interpreted as the default maximum version. */
+  if (version == 0) {
+    *out = TLS1_2_VERSION;
+    return 1;
+  }
+
+  return set_version_bound(method, out, version);
+}
+
+int SSL_CTX_set_min_proto_version(SSL_CTX *ctx, uint16_t version) {
+  return set_min_version(ctx->method, &ctx->conf_min_version, version);
+}
+
+int SSL_CTX_set_max_proto_version(SSL_CTX *ctx, uint16_t version) {
+  return set_max_version(ctx->method, &ctx->conf_max_version, version);
+}
+
+int SSL_set_min_proto_version(SSL *ssl, uint16_t version) {
+  return set_min_version(ssl->method, &ssl->conf_min_version, version);
+}
+
+int SSL_set_max_proto_version(SSL *ssl, uint16_t version) {
+  return set_max_version(ssl->method, &ssl->conf_max_version, version);
+}
+
+const struct {
+  uint16_t version;
+  uint32_t flag;
+} kProtocolVersions[] = {
+    {SSL3_VERSION, SSL_OP_NO_SSLv3},
+    {TLS1_VERSION, SSL_OP_NO_TLSv1},
+    {TLS1_1_VERSION, SSL_OP_NO_TLSv1_1},
+    {TLS1_2_VERSION, SSL_OP_NO_TLSv1_2},
+    {TLS1_3_VERSION, SSL_OP_NO_TLSv1_3},
+};
+
+int ssl_get_version_range(const SSL *ssl, uint16_t *out_min_version,
+                          uint16_t *out_max_version) {
+  /* For historical reasons, |SSL_OP_NO_DTLSv1| aliases |SSL_OP_NO_TLSv1|, but
+   * DTLS 1.0 should be mapped to TLS 1.1. */
+  uint32_t options = ssl->options;
+  if (SSL_is_dtls(ssl)) {
+    options &= ~SSL_OP_NO_TLSv1_1;
+    if (options & SSL_OP_NO_DTLSv1) {
+      options |= SSL_OP_NO_TLSv1_1;
+    }
+  }
+
+  uint16_t min_version = ssl->conf_min_version;
+  uint16_t max_version = ssl->conf_max_version;
+
+  /* OpenSSL's API for controlling versions entails blacklisting individual
+   * protocols. This has two problems. First, on the client, the protocol can
+   * only express a contiguous range of versions. Second, a library consumer
+   * trying to set a maximum version cannot disable protocol versions that get
+   * added in a future version of the library.
+   *
+   * To account for both of these, OpenSSL interprets the client-side bitmask
+   * as a min/max range by picking the lowest contiguous non-empty range of
+   * enabled protocols. Note that this means it is impossible to set a maximum
+   * version of the higest supported TLS version in a future-proof way. */
+  int any_enabled = 0;
+  for (size_t i = 0; i < OPENSSL_ARRAY_SIZE(kProtocolVersions); i++) {
+    /* Only look at the versions already enabled. */
+    if (min_version > kProtocolVersions[i].version) {
+      continue;
+    }
+    if (max_version < kProtocolVersions[i].version) {
+      break;
+    }
+
+    if (!(options & kProtocolVersions[i].flag)) {
+      /* The minimum version is the first enabled version. */
+      if (!any_enabled) {
+        any_enabled = 1;
+        min_version = kProtocolVersions[i].version;
+      }
+      continue;
+    }
+
+    /* If there is a disabled version after the first enabled one, all versions
+     * after it are implicitly disabled. */
+    if (any_enabled) {
+      max_version = kProtocolVersions[i-1].version;
+      break;
+    }
+  }
+
+  if (!any_enabled) {
+    OPENSSL_PUT_ERROR(SSL, SSL_R_NO_SUPPORTED_VERSIONS_ENABLED);
+    return 0;
+  }
+
+  *out_min_version = min_version;
+  *out_max_version = max_version;
+  return 1;
+}
+
+int SSL_version(const SSL *ssl) {
+  /* Report TLS 1.3 draft version as TLS 1.3 in the public API. */
+  if (ssl->version == TLS1_3_DRAFT_VERSION) {
+    return TLS1_3_VERSION;
+  }
+
+  return ssl->version;
+}
+
+static const char *ssl_get_version(int version) {
+  switch (version) {
+    /* Report TLS 1.3 draft version as TLS 1.3 in the public API. */
+    case TLS1_3_DRAFT_VERSION:
+      return "TLSv1.3";
+
+    case TLS1_2_VERSION:
+      return "TLSv1.2";
+
+    case TLS1_1_VERSION:
+      return "TLSv1.1";
+
+    case TLS1_VERSION:
+      return "TLSv1";
+
+    case SSL3_VERSION:
+      return "SSLv3";
+
+    case DTLS1_VERSION:
+      return "DTLSv1";
+
+    case DTLS1_2_VERSION:
+      return "DTLSv1.2";
+
+    default:
+      return "unknown";
+  }
+}
+
+const char *SSL_get_version(const SSL *ssl) {
+  return ssl_get_version(ssl->version);
+}
+
+const char *SSL_SESSION_get_version(const SSL_SESSION *session) {
+  return ssl_get_version(session->ssl_version);
+}
+
+uint16_t ssl3_protocol_version(const SSL *ssl) {
+  assert(ssl->s3->have_version);
+  uint16_t version;
+  if (!ssl_protocol_version_from_wire(&version, ssl->version)) {
+    /* |ssl->version| will always be set to a valid version. */
+    assert(0);
+    return 0;
+  }
+
+  return version;
+}
+
+int ssl_supports_version(SSL_HANDSHAKE *hs, uint16_t version) {
+  uint16_t protocol_version;
+  return method_supports_version(hs->ssl->method, version) &&
+         ssl_protocol_version_from_wire(&protocol_version, version) &&
+         hs->min_version <= protocol_version &&
+         protocol_version <= hs->max_version;
+}
+
+int ssl_add_supported_versions(SSL_HANDSHAKE *hs, CBB *cbb) {
+  const uint16_t *versions;
+  size_t num_versions;
+  get_method_versions(hs->ssl->method, &versions, &num_versions);
+  for (size_t i = 0; i < num_versions; i++) {
+    if (ssl_supports_version(hs, versions[i]) &&
+        !CBB_add_u16(cbb, versions[i])) {
+      return 0;
+    }
+  }
+  return 1;
+}
+
+int ssl_negotiate_version(SSL_HANDSHAKE *hs, uint8_t *out_alert,
+                          uint16_t *out_version, const CBS *peer_versions) {
+  const uint16_t *versions;
+  size_t num_versions;
+  get_method_versions(hs->ssl->method, &versions, &num_versions);
+  for (size_t i = 0; i < num_versions; i++) {
+    if (!ssl_supports_version(hs, versions[i])) {
+      continue;
+    }
+
+    CBS copy = *peer_versions;
+    while (CBS_len(&copy) != 0) {
+      uint16_t version;
+      if (!CBS_get_u16(&copy, &version)) {
+        OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
+        *out_alert = SSL_AD_DECODE_ERROR;
+        return 0;
+      }
+
+      if (version == versions[i]) {
+        *out_version = version;
+        return 1;
+      }
+    }
+  }
+
+  OPENSSL_PUT_ERROR(SSL, SSL_R_UNSUPPORTED_PROTOCOL);
+  *out_alert = SSL_AD_PROTOCOL_VERSION;
+  return 0;
+}