diff --git a/ssl/tls13_client.c b/ssl/tls13_client.c
new file mode 100644
index 0000000..cf8b390
--- /dev/null
+++ b/ssl/tls13_client.c
@@ -0,0 +1,462 @@
+/* Copyright (c) 2016, 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 <string.h>
+
+#include <openssl/bytestring.h>
+#include <openssl/digest.h>
+#include <openssl/err.h>
+#include <openssl/mem.h>
+#include <openssl/stack.h>
+#include <openssl/x509.h>
+
+#include "internal.h"
+
+
+enum client_hs_state_t {
+  state_process_server_hello = 0,
+  state_process_encrypted_extensions,
+  state_process_certificate_request,
+  state_process_server_certificate,
+  state_process_server_certificate_verify,
+  state_process_server_finished,
+  state_certificate_callback,
+  state_send_client_certificate,
+  state_send_client_certificate_verify,
+  state_complete_client_certificate_verify,
+  state_send_client_finished,
+  state_flush,
+  state_done,
+};
+
+static enum ssl_hs_wait_t do_process_server_hello(SSL *ssl, SSL_HANDSHAKE *hs) {
+  if (!tls13_check_message_type(ssl, SSL3_MT_SERVER_HELLO)) {
+    return ssl_hs_error;
+  }
+
+  CBS cbs, server_random, extensions;
+  uint16_t server_wire_version;
+  uint16_t cipher_suite;
+  CBS_init(&cbs, ssl->init_msg, ssl->init_num);
+  if (!CBS_get_u16(&cbs, &server_wire_version) ||
+      !CBS_get_bytes(&cbs, &server_random, SSL3_RANDOM_SIZE) ||
+      !CBS_get_u16(&cbs, &cipher_suite) ||
+      !CBS_get_u16_length_prefixed(&cbs, &extensions) ||
+      CBS_len(&cbs) != 0) {
+    ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
+    return ssl_hs_error;
+  }
+
+  /* Parse out the extensions. */
+  int have_key_share = 0;
+  CBS key_share;
+  while (CBS_len(&extensions) != 0) {
+    uint16_t type;
+    CBS extension;
+    if (!CBS_get_u16(&extensions, &type) ||
+        !CBS_get_u16_length_prefixed(&extensions, &extension)) {
+      OPENSSL_PUT_ERROR(SSL, SSL_R_PARSE_TLSEXT);
+      ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
+      return ssl_hs_error;
+    }
+
+    switch (type) {
+      case TLSEXT_TYPE_key_share:
+        if (have_key_share) {
+          OPENSSL_PUT_ERROR(SSL, SSL_R_DUPLICATE_EXTENSION);
+          ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
+          return ssl_hs_error;
+        }
+        key_share = extension;
+        have_key_share = 1;
+        break;
+      default:
+        OPENSSL_PUT_ERROR(SSL, SSL_R_UNEXPECTED_EXTENSION);
+        ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_UNSUPPORTED_EXTENSION);
+        return ssl_hs_error;
+    }
+  }
+
+  assert(ssl->s3->have_version);
+  memcpy(ssl->s3->server_random, CBS_data(&server_random), SSL3_RANDOM_SIZE);
+
+  ssl->hit = 0;
+  if (!ssl_get_new_session(ssl, 0)) {
+    ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
+    return ssl_hs_error;
+  }
+
+  const SSL_CIPHER *cipher = SSL_get_cipher_by_value(cipher_suite);
+  if (cipher == NULL) {
+    OPENSSL_PUT_ERROR(SSL, SSL_R_UNKNOWN_CIPHER_RETURNED);
+    ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
+    return ssl_hs_error;
+  }
+
+  /* Check if the cipher is disabled. */
+  if ((cipher->algorithm_mkey & ssl->cert->mask_k) ||
+      (cipher->algorithm_auth & ssl->cert->mask_a) ||
+      SSL_CIPHER_get_min_version(cipher) > ssl3_protocol_version(ssl) ||
+      SSL_CIPHER_get_max_version(cipher) < ssl3_protocol_version(ssl) ||
+      !sk_SSL_CIPHER_find(ssl_get_ciphers_by_id(ssl), NULL, cipher)) {
+    OPENSSL_PUT_ERROR(SSL, SSL_R_WRONG_CIPHER_RETURNED);
+    ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
+    return ssl_hs_error;
+  }
+
+  ssl->session->cipher = cipher;
+  ssl->s3->tmp.new_cipher = cipher;
+
+  /* The PRF hash is now known. Set up the key schedule. */
+  static const uint8_t kZeroes[EVP_MAX_MD_SIZE] = {0};
+  size_t hash_len =
+      EVP_MD_size(ssl_get_handshake_digest(ssl_get_algorithm_prf(ssl)));
+  if (!tls13_init_key_schedule(ssl, kZeroes, hash_len)) {
+    return ssl_hs_error;
+  }
+
+  /* Resolve PSK and incorporate it into the secret. */
+  if (cipher->algorithm_auth == SSL_aPSK) {
+    /* TODO(davidben): Support PSK. */
+    OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
+    return ssl_hs_error;
+  } else if (!tls13_advance_key_schedule(ssl, kZeroes, hash_len)) {
+    return ssl_hs_error;
+  }
+
+  /* Resolve ECDHE and incorporate it into the secret. */
+  if (cipher->algorithm_mkey == SSL_kECDHE) {
+    if (!have_key_share) {
+      OPENSSL_PUT_ERROR(SSL, SSL_R_MISSING_KEY_SHARE);
+      ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_MISSING_EXTENSION);
+      return ssl_hs_error;
+    }
+
+    uint8_t *dhe_secret;
+    size_t dhe_secret_len;
+    uint8_t alert = SSL_AD_DECODE_ERROR;
+    if (!ext_key_share_parse_serverhello(ssl, &dhe_secret, &dhe_secret_len,
+                                         &alert, &key_share)) {
+      ssl3_send_alert(ssl, SSL3_AL_FATAL, alert);
+      return ssl_hs_error;
+    }
+
+    int ok = tls13_advance_key_schedule(ssl, dhe_secret, dhe_secret_len);
+    OPENSSL_free(dhe_secret);
+    if (!ok) {
+      return ssl_hs_error;
+    }
+  } else {
+    if (have_key_share) {
+      OPENSSL_PUT_ERROR(SSL, SSL_R_UNEXPECTED_EXTENSION);
+      ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_UNSUPPORTED_EXTENSION);
+      return ssl_hs_error;
+    }
+    if (!tls13_advance_key_schedule(ssl, kZeroes, hash_len)) {
+      return ssl_hs_error;
+    }
+    return ssl_hs_error;
+  }
+
+  if (!tls13_set_handshake_traffic(ssl)) {
+    return ssl_hs_error;
+  }
+
+  hs->state = state_process_encrypted_extensions;
+  return ssl_hs_read_message;
+}
+
+static enum ssl_hs_wait_t do_process_encrypted_extensions(SSL *ssl,
+                                                          SSL_HANDSHAKE *hs) {
+  if (!tls13_check_message_type(ssl, SSL3_MT_ENCRYPTED_EXTENSIONS)) {
+    return ssl_hs_error;
+  }
+
+  CBS cbs;
+  CBS_init(&cbs, ssl->init_msg, ssl->init_num);
+  if (!ssl_parse_serverhello_tlsext(ssl, &cbs)) {
+    OPENSSL_PUT_ERROR(SSL, SSL_R_PARSE_TLSEXT);
+    return ssl_hs_error;
+  }
+  if (CBS_len(&cbs) != 0) {
+    OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
+    ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
+    return ssl_hs_error;
+  }
+
+  if (!ssl->method->hash_current_message(ssl)) {
+    return ssl_hs_error;
+  }
+
+  hs->state = state_process_certificate_request;
+  return ssl_hs_read_message;
+}
+
+static enum ssl_hs_wait_t do_process_certificate_request(SSL *ssl,
+                                                         SSL_HANDSHAKE *hs) {
+  ssl->s3->tmp.cert_request = 0;
+
+  /* CertificateRequest may only be sent in certificate-based ciphers. */
+  if (!ssl_cipher_uses_certificate_auth(ssl->s3->tmp.new_cipher)) {
+    hs->state = state_process_server_finished;
+    return ssl_hs_ok;
+  }
+
+  /* CertificateRequest is optional. */
+  if (ssl->s3->tmp.message_type != SSL3_MT_CERTIFICATE_REQUEST) {
+    hs->state = state_process_server_certificate;
+    return ssl_hs_ok;
+  }
+
+  CBS cbs, context, supported_signature_algorithms;
+  CBS_init(&cbs, ssl->init_msg, ssl->init_num);
+  if (!CBS_get_u8_length_prefixed(&cbs, &context) ||
+      !CBS_stow(&context, &ssl->s3->hs->cert_context,
+                &ssl->s3->hs->cert_context_len) ||
+      !CBS_get_u16_length_prefixed(&cbs, &supported_signature_algorithms) ||
+      !tls1_parse_peer_sigalgs(ssl, &supported_signature_algorithms)) {
+    ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
+    OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
+    return ssl_hs_error;
+  }
+
+  uint8_t alert;
+  STACK_OF(X509_NAME) *ca_sk = ssl_parse_client_CA_list(ssl, &alert, &cbs);
+  if (ca_sk == NULL) {
+    ssl3_send_alert(ssl, SSL3_AL_FATAL, alert);
+    return ssl_hs_error;
+  }
+
+  /* Ignore extensions. */
+  CBS extensions;
+  if (!CBS_get_u16_length_prefixed(&cbs, &extensions) ||
+      CBS_len(&cbs) != 0) {
+    ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
+    OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
+    return ssl_hs_error;
+  }
+
+  ssl->s3->tmp.cert_request = 1;
+  sk_X509_NAME_pop_free(ssl->s3->tmp.ca_names, X509_NAME_free);
+  ssl->s3->tmp.ca_names = ca_sk;
+
+  if (!ssl->method->hash_current_message(ssl)) {
+    return ssl_hs_error;
+  }
+
+  hs->state = state_process_server_certificate;
+  return ssl_hs_read_message;
+}
+
+static enum ssl_hs_wait_t do_process_server_certificate(SSL *ssl,
+                                                        SSL_HANDSHAKE *hs) {
+  if (!tls13_check_message_type(ssl, SSL3_MT_CERTIFICATE) ||
+      !tls13_process_certificate(ssl) ||
+      !ssl->method->hash_current_message(ssl)) {
+    return ssl_hs_error;
+  }
+
+  hs->state = state_process_server_certificate_verify;
+  return ssl_hs_read_message;
+}
+
+static enum ssl_hs_wait_t do_process_server_certificate_verify(
+    SSL *ssl, SSL_HANDSHAKE *hs) {
+  if (!tls13_check_message_type(ssl, SSL3_MT_CERTIFICATE_VERIFY) ||
+      !tls13_process_certificate_verify(ssl) ||
+      !ssl->method->hash_current_message(ssl)) {
+    return 0;
+  }
+
+  hs->state = state_process_server_finished;
+  return ssl_hs_read_message;
+}
+
+static enum ssl_hs_wait_t do_process_server_finished(SSL *ssl,
+                                                     SSL_HANDSHAKE *hs) {
+  static const uint8_t kZeroes[EVP_MAX_MD_SIZE] = {0};
+
+  if (!tls13_check_message_type(ssl, SSL3_MT_FINISHED) ||
+      !tls13_process_finished(ssl) ||
+      !ssl->method->hash_current_message(ssl) ||
+      /* Update the secret to the master secret and derive traffic keys. */
+      !tls13_advance_key_schedule(ssl, kZeroes, hs->hash_len) ||
+      !tls13_derive_traffic_secret_0(ssl)) {
+    return ssl_hs_error;
+  }
+
+  hs->state = state_certificate_callback;
+  return ssl_hs_ok;
+}
+
+static enum ssl_hs_wait_t do_certificate_callback(SSL *ssl, SSL_HANDSHAKE *hs) {
+  /* The peer didn't request a certificate. */
+  if (!ssl->s3->tmp.cert_request) {
+    hs->state = state_send_client_finished;
+    return ssl_hs_ok;
+  }
+
+  /* Call cert_cb to update the certificate. */
+  if (ssl->cert->cert_cb != NULL) {
+    int rv = ssl->cert->cert_cb(ssl, ssl->cert->cert_cb_arg);
+    if (rv == 0) {
+      ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
+      OPENSSL_PUT_ERROR(SSL, SSL_R_CERT_CB_ERROR);
+      return ssl_hs_error;
+    }
+    if (rv < 0) {
+      hs->state = state_certificate_callback;
+      return ssl_hs_x509_lookup;
+    }
+  }
+
+  hs->state = state_send_client_certificate;
+  return ssl_hs_ok;
+}
+
+static enum ssl_hs_wait_t do_send_client_certificate(SSL *ssl,
+                                                     SSL_HANDSHAKE *hs) {
+  if (!ssl_has_certificate(ssl) && ssl->ctx->client_cert_cb != NULL) {
+    X509 *x509 = NULL;
+    EVP_PKEY *pkey = NULL;
+    int rv = ssl->ctx->client_cert_cb(ssl, &x509, &pkey);
+    if (rv < 0) {
+      hs->state = state_send_client_certificate;
+      return ssl_hs_x509_lookup;
+    }
+
+    int setup_error = rv == 1 && (!SSL_use_certificate(ssl, x509) ||
+                                  !SSL_use_PrivateKey(ssl, pkey));
+    X509_free(x509);
+    EVP_PKEY_free(pkey);
+    if (setup_error) {
+      ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
+      return ssl_hs_error;
+    }
+  }
+
+  if (!tls13_prepare_certificate(ssl)) {
+    return ssl_hs_error;
+  }
+
+  hs->state = state_send_client_certificate_verify;
+  return ssl_hs_write_message;
+}
+
+static enum ssl_hs_wait_t do_send_client_certificate_verify(SSL *ssl,
+                                                            SSL_HANDSHAKE *hs,
+                                                            int is_first_run) {
+  /* Don't send CertificateVerify if there is no certificate. */
+  if (!ssl_has_certificate(ssl)) {
+    hs->state = state_send_client_finished;
+    return ssl_hs_ok;
+  }
+
+  switch (tls13_prepare_certificate_verify(ssl, is_first_run)) {
+    case ssl_private_key_success:
+      hs->state = state_send_client_finished;
+      return ssl_hs_write_message;
+
+    case ssl_private_key_retry:
+      hs->state = state_complete_client_certificate_verify;
+      return ssl_hs_private_key_operation;
+
+    case ssl_private_key_failure:
+      return ssl_hs_error;
+  }
+
+  assert(0);
+  return ssl_hs_error;
+}
+
+static enum ssl_hs_wait_t do_send_client_finished(SSL *ssl, SSL_HANDSHAKE *hs) {
+  if (!tls13_prepare_finished(ssl)) {
+    return ssl_hs_error;
+  }
+
+  hs->state = state_flush;
+  return ssl_hs_write_message;
+}
+
+static enum ssl_hs_wait_t do_flush(SSL *ssl, SSL_HANDSHAKE *hs) {
+  if (!tls13_set_traffic_key(ssl, type_data, evp_aead_open,
+                             hs->traffic_secret_0, hs->hash_len) ||
+      !tls13_set_traffic_key(ssl, type_data, evp_aead_seal,
+                             hs->traffic_secret_0, hs->hash_len) ||
+      !tls13_finalize_keys(ssl)) {
+    return ssl_hs_error;
+  }
+
+  hs->state = state_done;
+  return ssl_hs_flush;
+}
+
+enum ssl_hs_wait_t tls13_client_handshake(SSL *ssl) {
+  SSL_HANDSHAKE *hs = ssl->s3->hs;
+
+  while (hs->state != state_done) {
+    enum ssl_hs_wait_t ret = ssl_hs_error;
+    enum client_hs_state_t state = hs->state;
+    switch (state) {
+      case state_process_server_hello:
+        ret = do_process_server_hello(ssl, hs);
+        break;
+      case state_process_encrypted_extensions:
+        ret = do_process_encrypted_extensions(ssl, hs);
+        break;
+      case state_process_certificate_request:
+        ret = do_process_certificate_request(ssl, hs);
+        break;
+      case state_process_server_certificate:
+        ret = do_process_server_certificate(ssl, hs);
+        break;
+      case state_process_server_certificate_verify:
+        ret = do_process_server_certificate_verify(ssl, hs);
+        break;
+      case state_process_server_finished:
+        ret = do_process_server_finished(ssl, hs);
+        break;
+      case state_certificate_callback:
+        ret = do_certificate_callback(ssl, hs);
+        break;
+      case state_send_client_certificate:
+        ret = do_send_client_certificate(ssl, hs);
+        break;
+      case state_send_client_certificate_verify:
+        ret = do_send_client_certificate_verify(ssl, hs, 1 /* first run */);
+      break;
+      case state_complete_client_certificate_verify:
+        ret = do_send_client_certificate_verify(ssl, hs, 0 /* complete */);
+      break;
+      case state_send_client_finished:
+        ret = do_send_client_finished(ssl, hs);
+        break;
+      case state_flush:
+        ret = do_flush(ssl, hs);
+        break;
+      case state_done:
+        ret = ssl_hs_ok;
+        break;
+    }
+
+    if (ret != ssl_hs_ok) {
+      return ret;
+    }
+  }
+
+  return ssl_hs_ok;
+}