diff --git a/library/ssl_cookie.c b/library/ssl_cookie.c
new file mode 100644
index 0000000..56e9bdd
--- /dev/null
+++ b/library/ssl_cookie.c
@@ -0,0 +1,256 @@
+/*
+ *  DTLS cookie callbacks implementation
+ *
+ *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *  This file is part of mbed TLS (https://tls.mbed.org)
+ */
+/*
+ * These session callbacks use a simple chained list
+ * to store and retrieve the session information.
+ */
+
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "mbedtls/config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
+#if defined(MBEDTLS_SSL_COOKIE_C)
+
+#if defined(MBEDTLS_PLATFORM_C)
+#include "mbedtls/platform.h"
+#else
+#define mbedtls_calloc    calloc
+#define mbedtls_free      free
+#endif
+
+#include "mbedtls/ssl_cookie.h"
+#include "mbedtls/ssl_internal.h"
+#include "mbedtls/platform_util.h"
+
+#include <string.h>
+
+/*
+ * If DTLS is in use, then at least one of SHA-1, SHA-256, SHA-512 is
+ * available. Try SHA-256 first, 512 wastes resources since we need to stay
+ * with max 32 bytes of cookie for DTLS 1.0
+ */
+#if defined(MBEDTLS_SHA256_C)
+#define COOKIE_MD           MBEDTLS_MD_SHA224
+#define COOKIE_MD_OUTLEN    32
+#define COOKIE_HMAC_LEN     28
+#elif defined(MBEDTLS_SHA512_C)
+#define COOKIE_MD           MBEDTLS_MD_SHA384
+#define COOKIE_MD_OUTLEN    48
+#define COOKIE_HMAC_LEN     28
+#elif defined(MBEDTLS_SHA1_C)
+#define COOKIE_MD           MBEDTLS_MD_SHA1
+#define COOKIE_MD_OUTLEN    20
+#define COOKIE_HMAC_LEN     20
+#else
+#error "DTLS hello verify needs SHA-1 or SHA-2"
+#endif
+
+/*
+ * Cookies are formed of a 4-bytes timestamp (or serial number) and
+ * an HMAC of timestemp and client ID.
+ */
+#define COOKIE_LEN      ( 4 + COOKIE_HMAC_LEN )
+
+void mbedtls_ssl_cookie_init( mbedtls_ssl_cookie_ctx *ctx )
+{
+    mbedtls_md_init( &ctx->hmac_ctx );
+#if !defined(MBEDTLS_HAVE_TIME)
+    ctx->serial = 0;
+#endif
+    ctx->timeout = MBEDTLS_SSL_COOKIE_TIMEOUT;
+
+#if defined(MBEDTLS_THREADING_C)
+    mbedtls_mutex_init( &ctx->mutex );
+#endif
+}
+
+void mbedtls_ssl_cookie_set_timeout( mbedtls_ssl_cookie_ctx *ctx, unsigned long delay )
+{
+    ctx->timeout = delay;
+}
+
+void mbedtls_ssl_cookie_free( mbedtls_ssl_cookie_ctx *ctx )
+{
+    mbedtls_md_free( &ctx->hmac_ctx );
+
+#if defined(MBEDTLS_THREADING_C)
+    mbedtls_mutex_free( &ctx->mutex );
+#endif
+
+    mbedtls_platform_zeroize( ctx, sizeof( mbedtls_ssl_cookie_ctx ) );
+}
+
+int mbedtls_ssl_cookie_setup( mbedtls_ssl_cookie_ctx *ctx,
+                      int (*f_rng)(void *, unsigned char *, size_t),
+                      void *p_rng )
+{
+    int ret;
+    unsigned char key[COOKIE_MD_OUTLEN];
+
+    if( ( ret = f_rng( p_rng, key, sizeof( key ) ) ) != 0 )
+        return( ret );
+
+    ret = mbedtls_md_setup( &ctx->hmac_ctx, mbedtls_md_info_from_type( COOKIE_MD ), 1 );
+    if( ret != 0 )
+        return( ret );
+
+    ret = mbedtls_md_hmac_starts( &ctx->hmac_ctx, key, sizeof( key ) );
+    if( ret != 0 )
+        return( ret );
+
+    mbedtls_platform_zeroize( key, sizeof( key ) );
+
+    return( 0 );
+}
+
+/*
+ * Generate the HMAC part of a cookie
+ */
+static int ssl_cookie_hmac( mbedtls_md_context_t *hmac_ctx,
+                            const unsigned char time[4],
+                            unsigned char **p, unsigned char *end,
+                            const unsigned char *cli_id, size_t cli_id_len )
+{
+    unsigned char hmac_out[COOKIE_MD_OUTLEN];
+
+    if( (size_t)( end - *p ) < COOKIE_HMAC_LEN )
+        return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
+
+    if( mbedtls_md_hmac_reset(  hmac_ctx ) != 0 ||
+        mbedtls_md_hmac_update( hmac_ctx, time, 4 ) != 0 ||
+        mbedtls_md_hmac_update( hmac_ctx, cli_id, cli_id_len ) != 0 ||
+        mbedtls_md_hmac_finish( hmac_ctx, hmac_out ) != 0 )
+    {
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+    }
+
+    memcpy( *p, hmac_out, COOKIE_HMAC_LEN );
+    *p += COOKIE_HMAC_LEN;
+
+    return( 0 );
+}
+
+/*
+ * Generate cookie for DTLS ClientHello verification
+ */
+int mbedtls_ssl_cookie_write( void *p_ctx,
+                      unsigned char **p, unsigned char *end,
+                      const unsigned char *cli_id, size_t cli_id_len )
+{
+    int ret;
+    mbedtls_ssl_cookie_ctx *ctx = (mbedtls_ssl_cookie_ctx *) p_ctx;
+    unsigned long t;
+
+    if( ctx == NULL || cli_id == NULL )
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+
+    if( (size_t)( end - *p ) < COOKIE_LEN )
+        return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
+
+#if defined(MBEDTLS_HAVE_TIME)
+    t = (unsigned long) mbedtls_time( NULL );
+#else
+    t = ctx->serial++;
+#endif
+
+    (*p)[0] = (unsigned char)( t >> 24 );
+    (*p)[1] = (unsigned char)( t >> 16 );
+    (*p)[2] = (unsigned char)( t >>  8 );
+    (*p)[3] = (unsigned char)( t       );
+    *p += 4;
+
+#if defined(MBEDTLS_THREADING_C)
+    if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR + ret );
+#endif
+
+    ret = ssl_cookie_hmac( &ctx->hmac_ctx, *p - 4,
+                           p, end, cli_id, cli_id_len );
+
+#if defined(MBEDTLS_THREADING_C)
+    if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR +
+                MBEDTLS_ERR_THREADING_MUTEX_ERROR );
+#endif
+
+    return( ret );
+}
+
+/*
+ * Check a cookie
+ */
+int mbedtls_ssl_cookie_check( void *p_ctx,
+                      const unsigned char *cookie, size_t cookie_len,
+                      const unsigned char *cli_id, size_t cli_id_len )
+{
+    unsigned char ref_hmac[COOKIE_HMAC_LEN];
+    int ret = 0;
+    unsigned char *p = ref_hmac;
+    mbedtls_ssl_cookie_ctx *ctx = (mbedtls_ssl_cookie_ctx *) p_ctx;
+    unsigned long cur_time, cookie_time;
+
+    if( ctx == NULL || cli_id == NULL )
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+
+    if( cookie_len != COOKIE_LEN )
+        return( -1 );
+
+#if defined(MBEDTLS_THREADING_C)
+    if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR + ret );
+#endif
+
+    if( ssl_cookie_hmac( &ctx->hmac_ctx, cookie,
+                         &p, p + sizeof( ref_hmac ),
+                         cli_id, cli_id_len ) != 0 )
+        ret = -1;
+
+#if defined(MBEDTLS_THREADING_C)
+    if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR +
+                MBEDTLS_ERR_THREADING_MUTEX_ERROR );
+#endif
+
+    if( ret != 0 )
+        return( ret );
+
+    if( mbedtls_ssl_safer_memcmp( cookie + 4, ref_hmac, sizeof( ref_hmac ) ) != 0 )
+        return( -1 );
+
+#if defined(MBEDTLS_HAVE_TIME)
+    cur_time = (unsigned long) mbedtls_time( NULL );
+#else
+    cur_time = ctx->serial;
+#endif
+
+    cookie_time = ( (unsigned long) cookie[0] << 24 ) |
+                  ( (unsigned long) cookie[1] << 16 ) |
+                  ( (unsigned long) cookie[2] <<  8 ) |
+                  ( (unsigned long) cookie[3]       );
+
+    if( ctx->timeout != 0 && cur_time - cookie_time > ctx->timeout )
+        return( -1 );
+
+    return( 0 );
+}
+#endif /* MBEDTLS_SSL_COOKIE_C */