Diff: SSL/library/cipher.c

Revision:

0:796d0f61a05b

diff -r 000000000000 -r 796d0f61a05b SSL/library/cipher.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/SSL/library/cipher.c	Thu Sep 27 06:34:22 2018 +0000
@@ -0,0 +1,790 @@
+/**
+ * \file cipher.c
+ *
+ * \brief Generic cipher wrapper for PolarSSL
+ *
+ * \author Adriaan de Jong <dejong@fox-it.com>
+ *
+ *  Copyright (C) 2006-2014, Brainspark B.V.
+ *
+ *  This file is part of PolarSSL (http://www.polarssl.org)
+ *  Lead Maintainer: Paul Bakker <polarssl_maintainer at polarssl.org>
+ *
+ *  All rights reserved.
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License along
+ *  with this program; if not, write to the Free Software Foundation, Inc.,
+ *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#if !defined(POLARSSL_CONFIG_FILE)
+#include "polarssl/config.h"
+#else
+#include POLARSSL_CONFIG_FILE
+#endif
+
+#if defined(POLARSSL_CIPHER_C)
+
+#include "polarssl/cipher.h"
+#include "polarssl/cipher_wrap.h"
+
+#if defined(POLARSSL_GCM_C)
+#include "polarssl/gcm.h"
+#endif
+
+#include <stdlib.h>
+
+#if defined(POLARSSL_ARC4_C) || defined(POLARSSL_CIPHER_NULL_CIPHER)
+#define POLARSSL_CIPHER_MODE_STREAM
+#endif
+
+#if defined(_MSC_VER) && !defined strcasecmp && !defined(EFIX64) && \
+    !defined(EFI32)
+#define strcasecmp _stricmp
+#endif
+
+static int supported_init = 0;
+
+const int *cipher_list( void )
+{
+    const cipher_definition_t *def;
+    int *type;
+
+    if( ! supported_init )
+    {
+        def = cipher_definitions;
+        type = supported_ciphers;
+
+        while( def->type != 0 )
+            *type++ = (*def++).type;
+
+        *type = 0;
+
+        supported_init = 1;
+    }
+
+    return supported_ciphers;
+}
+
+const cipher_info_t *cipher_info_from_type( const cipher_type_t cipher_type )
+{
+    const cipher_definition_t *def;
+
+    for( def = cipher_definitions; def->info != NULL; def++ )
+        if( def->type == cipher_type )
+            return( def->info );
+
+    return NULL;
+}
+
+const cipher_info_t *cipher_info_from_string( const char *cipher_name )
+{
+    const cipher_definition_t *def;
+
+    if( NULL == cipher_name )
+        return NULL;
+
+    for( def = cipher_definitions; def->info != NULL; def++ )
+        if( !  strcasecmp( def->info->name, cipher_name ) )
+            return( def->info );
+
+    return NULL;
+}
+
+const cipher_info_t *cipher_info_from_values( const cipher_id_t cipher_id,
+                                              int key_length,
+                                              const cipher_mode_t mode )
+{
+    const cipher_definition_t *def;
+
+    for( def = cipher_definitions; def->info != NULL; def++ )
+        if( def->info->base->cipher == cipher_id &&
+            def->info->key_length == (unsigned) key_length &&
+            def->info->mode == mode )
+            return( def->info );
+
+    return NULL;
+}
+
+int cipher_init_ctx( cipher_context_t *ctx, const cipher_info_t *cipher_info )
+{
+    if( NULL == cipher_info || NULL == ctx )
+        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+
+    memset( ctx, 0, sizeof( cipher_context_t ) );
+
+    if( NULL == ( ctx->cipher_ctx = cipher_info->base->ctx_alloc_func() ) )
+        return POLARSSL_ERR_CIPHER_ALLOC_FAILED;
+
+    ctx->cipher_info = cipher_info;
+
+#if defined(POLARSSL_CIPHER_MODE_WITH_PADDING)
+    /*
+     * Ignore possible errors caused by a cipher mode that doesn't use padding
+     */
+#if defined(POLARSSL_CIPHER_PADDING_PKCS7)
+    (void) cipher_set_padding_mode( ctx, POLARSSL_PADDING_PKCS7 );
+#else
+    (void) cipher_set_padding_mode( ctx, POLARSSL_PADDING_NONE );
+#endif
+#endif /* POLARSSL_CIPHER_MODE_WITH_PADDING */
+
+    return 0;
+}
+
+int cipher_free_ctx( cipher_context_t *ctx )
+{
+    if( ctx == NULL || ctx->cipher_info == NULL )
+        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+
+    ctx->cipher_info->base->ctx_free_func( ctx->cipher_ctx );
+
+    return 0;
+}
+
+int cipher_setkey( cipher_context_t *ctx, const unsigned char *key,
+        int key_length, const operation_t operation )
+{
+    if( NULL == ctx || NULL == ctx->cipher_info )
+        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+
+    if( (int) ctx->cipher_info->key_length != key_length )
+        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+
+    ctx->key_length = key_length;
+    ctx->operation = operation;
+
+    /*
+     * For CFB and CTR mode always use the encryption key schedule
+     */
+    if( POLARSSL_ENCRYPT == operation ||
+        POLARSSL_MODE_CFB == ctx->cipher_info->mode ||
+        POLARSSL_MODE_CTR == ctx->cipher_info->mode )
+    {
+        return ctx->cipher_info->base->setkey_enc_func( ctx->cipher_ctx, key,
+                ctx->key_length );
+    }
+
+    if( POLARSSL_DECRYPT == operation )
+        return ctx->cipher_info->base->setkey_dec_func( ctx->cipher_ctx, key,
+                ctx->key_length );
+
+    return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+}
+
+int cipher_set_iv( cipher_context_t *ctx,
+                   const unsigned char *iv, size_t iv_len )
+{
+    size_t actual_iv_size;
+
+    if( NULL == ctx || NULL == ctx->cipher_info || NULL == iv )
+        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+
+    /* avoid buffer overflow in ctx->iv */
+    if( iv_len > POLARSSL_MAX_IV_LENGTH )
+        return POLARSSL_ERR_CIPHER_FEATURE_UNAVAILABLE;
+
+    if( ctx->cipher_info->accepts_variable_iv_size )
+        actual_iv_size = iv_len;
+    else
+    {
+        actual_iv_size = ctx->cipher_info->iv_size;
+
+        /* avoid reading past the end of input buffer */
+        if( actual_iv_size > iv_len )
+            return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+    }
+
+    memcpy( ctx->iv, iv, actual_iv_size );
+    ctx->iv_size = actual_iv_size;
+
+    return 0;
+}
+
+int cipher_reset( cipher_context_t *ctx )
+{
+    if( NULL == ctx || NULL == ctx->cipher_info )
+        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+
+    ctx->unprocessed_len = 0;
+
+    return 0;
+}
+
+#if defined(POLARSSL_CIPHER_MODE_AEAD)
+int cipher_update_ad( cipher_context_t *ctx,
+                      const unsigned char *ad, size_t ad_len )
+{
+    if( NULL == ctx || NULL == ctx->cipher_info )
+        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+
+#if defined(POLARSSL_GCM_C)
+    if( POLARSSL_MODE_GCM == ctx->cipher_info->mode )
+    {
+        return gcm_starts( (gcm_context *) ctx->cipher_ctx, ctx->operation,
+                           ctx->iv, ctx->iv_size, ad, ad_len );
+    }
+#endif
+
+    return 0;
+}
+#endif /* POLARSSL_CIPHER_MODE_AEAD */
+
+int cipher_update( cipher_context_t *ctx, const unsigned char *input,
+                   size_t ilen, unsigned char *output, size_t *olen )
+{
+    int ret;
+
+    if( NULL == ctx || NULL == ctx->cipher_info || NULL == olen )
+    {
+        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+    }
+
+    *olen = 0;
+
+    if( ctx->cipher_info->mode == POLARSSL_MODE_ECB )
+    {
+        if( ilen != cipher_get_block_size( ctx ) )
+            return POLARSSL_ERR_CIPHER_FULL_BLOCK_EXPECTED;
+
+        *olen = ilen;
+
+        if( 0 != ( ret = ctx->cipher_info->base->ecb_func( ctx->cipher_ctx,
+                    ctx->operation, input, output ) ) )
+        {
+            return ret;
+        }
+
+        return 0;
+    }
+
+#if defined(POLARSSL_GCM_C)
+    if( ctx->cipher_info->mode == POLARSSL_MODE_GCM )
+    {
+        *olen = ilen;
+        return gcm_update( (gcm_context *) ctx->cipher_ctx, ilen, input,
+                           output );
+    }
+#endif
+
+    if( input == output &&
+       ( ctx->unprocessed_len != 0 || ilen % cipher_get_block_size( ctx ) ) )
+    {
+        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+    }
+
+#if defined(POLARSSL_CIPHER_MODE_CBC)
+    if( ctx->cipher_info->mode == POLARSSL_MODE_CBC )
+    {
+        size_t copy_len = 0;
+
+        /*
+         * If there is not enough data for a full block, cache it.
+         */
+        if( ( ctx->operation == POLARSSL_DECRYPT &&
+                ilen + ctx->unprocessed_len <= cipher_get_block_size( ctx ) ) ||
+             ( ctx->operation == POLARSSL_ENCRYPT &&
+                ilen + ctx->unprocessed_len < cipher_get_block_size( ctx ) ) )
+        {
+            memcpy( &( ctx->unprocessed_data[ctx->unprocessed_len] ), input,
+                    ilen );
+
+            ctx->unprocessed_len += ilen;
+            return 0;
+        }
+
+        /*
+         * Process cached data first
+         */
+        if( ctx->unprocessed_len != 0 )
+        {
+            copy_len = cipher_get_block_size( ctx ) - ctx->unprocessed_len;
+
+            memcpy( &( ctx->unprocessed_data[ctx->unprocessed_len] ), input,
+                    copy_len );
+
+            if( 0 != ( ret = ctx->cipher_info->base->cbc_func( ctx->cipher_ctx,
+                    ctx->operation, cipher_get_block_size( ctx ), ctx->iv,
+                    ctx->unprocessed_data, output ) ) )
+            {
+                return ret;
+            }
+
+            *olen += cipher_get_block_size( ctx );
+            output += cipher_get_block_size( ctx );
+            ctx->unprocessed_len = 0;
+
+            input += copy_len;
+            ilen -= copy_len;
+        }
+
+        /*
+         * Cache final, incomplete block
+         */
+        if( 0 != ilen )
+        {
+            copy_len = ilen % cipher_get_block_size( ctx );
+            if( copy_len == 0 && ctx->operation == POLARSSL_DECRYPT )
+                copy_len = cipher_get_block_size(ctx);
+
+            memcpy( ctx->unprocessed_data, &( input[ilen - copy_len] ),
+                    copy_len );
+
+            ctx->unprocessed_len += copy_len;
+            ilen -= copy_len;
+        }
+
+        /*
+         * Process remaining full blocks
+         */
+        if( ilen )
+        {
+            if( 0 != ( ret = ctx->cipher_info->base->cbc_func( ctx->cipher_ctx,
+                    ctx->operation, ilen, ctx->iv, input, output ) ) )
+            {
+                return ret;
+            }
+
+            *olen += ilen;
+        }
+
+        return 0;
+    }
+#endif /* POLARSSL_CIPHER_MODE_CBC */
+
+#if defined(POLARSSL_CIPHER_MODE_CFB)
+    if( ctx->cipher_info->mode == POLARSSL_MODE_CFB )
+    {
+        if( 0 != ( ret = ctx->cipher_info->base->cfb_func( ctx->cipher_ctx,
+                ctx->operation, ilen, &ctx->unprocessed_len, ctx->iv,
+                input, output ) ) )
+        {
+            return ret;
+        }
+
+        *olen = ilen;
+
+        return 0;
+    }
+#endif /* POLARSSL_CIPHER_MODE_CFB */
+
+#if defined(POLARSSL_CIPHER_MODE_CTR)
+    if( ctx->cipher_info->mode == POLARSSL_MODE_CTR )
+    {
+        if( 0 != ( ret = ctx->cipher_info->base->ctr_func( ctx->cipher_ctx,
+                ilen, &ctx->unprocessed_len, ctx->iv,
+                ctx->unprocessed_data, input, output ) ) )
+        {
+            return ret;
+        }
+
+        *olen = ilen;
+
+        return 0;
+    }
+#endif /* POLARSSL_CIPHER_MODE_CTR */
+
+#if defined(POLARSSL_CIPHER_MODE_STREAM)
+    if( ctx->cipher_info->mode == POLARSSL_MODE_STREAM )
+    {
+        if( 0 != ( ret = ctx->cipher_info->base->stream_func( ctx->cipher_ctx,
+                                                    ilen, input, output ) ) )
+        {
+            return ret;
+        }
+
+        *olen = ilen;
+
+        return 0;
+    }
+#endif /* POLARSSL_CIPHER_MODE_STREAM */
+
+    return POLARSSL_ERR_CIPHER_FEATURE_UNAVAILABLE;
+}
+
+#if defined(POLARSSL_CIPHER_MODE_WITH_PADDING)
+#if defined(POLARSSL_CIPHER_PADDING_PKCS7)
+/*
+ * PKCS7 (and PKCS5) padding: fill with ll bytes, with ll = padding_len
+ */
+static void add_pkcs_padding( unsigned char *output, size_t output_len,
+        size_t data_len )
+{
+    size_t padding_len = output_len - data_len;
+    unsigned char i;
+
+    for( i = 0; i < padding_len; i++ )
+        output[data_len + i] = (unsigned char) padding_len;
+}
+
+static int get_pkcs_padding( unsigned char *input, size_t input_len,
+        size_t *data_len )
+{
+    size_t i, pad_idx;
+    unsigned char padding_len, bad = 0;
+
+    if( NULL == input || NULL == data_len )
+        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+
+    padding_len = input[input_len - 1];
+    *data_len = input_len - padding_len;
+
+    /* Avoid logical || since it results in a branch */
+    bad |= padding_len > input_len;
+    bad |= padding_len == 0;
+
+    /* The number of bytes checked must be independent of padding_len,
+     * so pick input_len, which is usually 8 or 16 (one block) */
+    pad_idx = input_len - padding_len;
+    for( i = 0; i < input_len; i++ )
+        bad |= ( input[i] ^ padding_len ) * ( i >= pad_idx );
+
+    return POLARSSL_ERR_CIPHER_INVALID_PADDING * (bad != 0);
+}
+#endif /* POLARSSL_CIPHER_PADDING_PKCS7 */
+
+#if defined(POLARSSL_CIPHER_PADDING_ONE_AND_ZEROS)
+/*
+ * One and zeros padding: fill with 80 00 ... 00
+ */
+static void add_one_and_zeros_padding( unsigned char *output,
+                                       size_t output_len, size_t data_len )
+{
+    size_t padding_len = output_len - data_len;
+    unsigned char i = 0;
+
+    output[data_len] = 0x80;
+    for( i = 1; i < padding_len; i++ )
+        output[data_len + i] = 0x00;
+}
+
+static int get_one_and_zeros_padding( unsigned char *input, size_t input_len,
+                                      size_t *data_len )
+{
+    size_t i;
+    unsigned char done = 0, prev_done, bad;
+
+    if( NULL == input || NULL == data_len )
+        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+
+    bad = 0xFF;
+    *data_len = 0;
+    for( i = input_len; i > 0; i-- )
+    {
+        prev_done = done;
+        done |= ( input[i-1] != 0 );
+        *data_len |= ( i - 1 ) * ( done != prev_done );
+        bad &= ( input[i-1] ^ 0x80 ) | ( done == prev_done );
+    }
+
+    return POLARSSL_ERR_CIPHER_INVALID_PADDING * (bad != 0);
+
+}
+#endif /* POLARSSL_CIPHER_PADDING_ONE_AND_ZEROS */
+
+#if defined(POLARSSL_CIPHER_PADDING_ZEROS_AND_LEN)
+/*
+ * Zeros and len padding: fill with 00 ... 00 ll, where ll is padding length
+ */
+static void add_zeros_and_len_padding( unsigned char *output,
+                                       size_t output_len, size_t data_len )
+{
+    size_t padding_len = output_len - data_len;
+    unsigned char i = 0;
+
+    for( i = 1; i < padding_len; i++ )
+        output[data_len + i - 1] = 0x00;
+    output[output_len - 1] = (unsigned char) padding_len;
+}
+
+static int get_zeros_and_len_padding( unsigned char *input, size_t input_len,
+                                      size_t *data_len )
+{
+    size_t i, pad_idx;
+    unsigned char padding_len, bad = 0;
+
+    if( NULL == input || NULL == data_len )
+        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+
+    padding_len = input[input_len - 1];
+    *data_len = input_len - padding_len;
+
+    /* Avoid logical || since it results in a branch */
+    bad |= padding_len > input_len;
+    bad |= padding_len == 0;
+
+    /* The number of bytes checked must be independent of padding_len */
+    pad_idx = input_len - padding_len;
+    for( i = 0; i < input_len - 1; i++ )
+        bad |= input[i] * ( i >= pad_idx );
+
+    return POLARSSL_ERR_CIPHER_INVALID_PADDING * (bad != 0);
+}
+#endif /* POLARSSL_CIPHER_PADDING_ZEROS_AND_LEN */
+
+#if defined(POLARSSL_CIPHER_PADDING_ZEROS)
+/*
+ * Zero padding: fill with 00 ... 00
+ */
+static void add_zeros_padding( unsigned char *output,
+                               size_t output_len, size_t data_len )
+{
+    size_t i;
+
+    for( i = data_len; i < output_len; i++ )
+        output[i] = 0x00;
+}
+
+static int get_zeros_padding( unsigned char *input, size_t input_len,
+                              size_t *data_len )
+{
+    size_t i;
+    unsigned char done = 0, prev_done;
+
+    if( NULL == input || NULL == data_len )
+        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+
+    *data_len = 0;
+    for( i = input_len; i > 0; i-- )
+    {
+        prev_done = done;
+        done |= ( input[i-1] != 0 );
+        *data_len |= i * ( done != prev_done );
+    }
+
+    return 0;
+}
+#endif /* POLARSSL_CIPHER_PADDING_ZEROS */
+
+/*
+ * No padding: don't pad :)
+ *
+ * There is no add_padding function (check for NULL in cipher_finish)
+ * but a trivial get_padding function
+ */
+static int get_no_padding( unsigned char *input, size_t input_len,
+                              size_t *data_len )
+{
+    if( NULL == input || NULL == data_len )
+        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+
+    *data_len = input_len;
+
+    return 0;
+}
+#endif /* POLARSSL_CIPHER_MODE_WITH_PADDING */
+
+int cipher_finish( cipher_context_t *ctx,
+                   unsigned char *output, size_t *olen )
+{
+    if( NULL == ctx || NULL == ctx->cipher_info || NULL == olen )
+        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+
+    *olen = 0;
+
+    if( POLARSSL_MODE_CFB == ctx->cipher_info->mode ||
+        POLARSSL_MODE_CTR == ctx->cipher_info->mode ||
+        POLARSSL_MODE_GCM == ctx->cipher_info->mode ||
+        POLARSSL_MODE_STREAM == ctx->cipher_info->mode )
+    {
+        return 0;
+    }
+
+    if( POLARSSL_MODE_ECB == ctx->cipher_info->mode )
+    {
+        if( ctx->unprocessed_len != 0 )
+            return POLARSSL_ERR_CIPHER_FULL_BLOCK_EXPECTED;
+
+        return 0;
+    }
+
+#if defined(POLARSSL_CIPHER_MODE_CBC)
+    if( POLARSSL_MODE_CBC == ctx->cipher_info->mode )
+    {
+        int ret = 0;
+
+        if( POLARSSL_ENCRYPT == ctx->operation )
+        {
+            /* check for 'no padding' mode */
+            if( NULL == ctx->add_padding )
+            {
+                if( 0 != ctx->unprocessed_len )
+                    return POLARSSL_ERR_CIPHER_FULL_BLOCK_EXPECTED;
+
+                return 0;
+            }
+
+            ctx->add_padding( ctx->unprocessed_data, cipher_get_iv_size( ctx ),
+                    ctx->unprocessed_len );
+        }
+        else if ( cipher_get_block_size( ctx ) != ctx->unprocessed_len )
+        {
+            /*
+             * For decrypt operations, expect a full block,
+             * or an empty block if no padding
+             */
+            if( NULL == ctx->add_padding && 0 == ctx->unprocessed_len )
+                return 0;
+
+            return POLARSSL_ERR_CIPHER_FULL_BLOCK_EXPECTED;
+        }
+
+        /* cipher block */
+        if( 0 != ( ret = ctx->cipher_info->base->cbc_func( ctx->cipher_ctx,
+                ctx->operation, cipher_get_block_size( ctx ), ctx->iv,
+                ctx->unprocessed_data, output ) ) )
+        {
+            return ret;
+        }
+
+        /* Set output size for decryption */
+        if( POLARSSL_DECRYPT == ctx->operation )
+            return ctx->get_padding( output, cipher_get_block_size( ctx ),
+                                     olen );
+
+        /* Set output size for encryption */
+        *olen = cipher_get_block_size( ctx );
+        return 0;
+    }
+#else
+    ((void) output);
+#endif /* POLARSSL_CIPHER_MODE_CBC */
+
+    return POLARSSL_ERR_CIPHER_FEATURE_UNAVAILABLE;
+}
+
+#if defined(POLARSSL_CIPHER_MODE_WITH_PADDING)
+int cipher_set_padding_mode( cipher_context_t *ctx, cipher_padding_t mode )
+{
+    if( NULL == ctx ||
+        POLARSSL_MODE_CBC != ctx->cipher_info->mode )
+    {
+        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+    }
+
+    switch( mode )
+    {
+#if defined(POLARSSL_CIPHER_PADDING_PKCS7)
+    case POLARSSL_PADDING_PKCS7:
+        ctx->add_padding = add_pkcs_padding;
+        ctx->get_padding = get_pkcs_padding;
+        break;
+#endif
+#if defined(POLARSSL_CIPHER_PADDING_ONE_AND_ZEROS)
+    case POLARSSL_PADDING_ONE_AND_ZEROS:
+        ctx->add_padding = add_one_and_zeros_padding;
+        ctx->get_padding = get_one_and_zeros_padding;
+        break;
+#endif
+#if defined(POLARSSL_CIPHER_PADDING_ZEROS_AND_LEN)
+    case POLARSSL_PADDING_ZEROS_AND_LEN:
+        ctx->add_padding = add_zeros_and_len_padding;
+        ctx->get_padding = get_zeros_and_len_padding;
+        break;
+#endif
+#if defined(POLARSSL_CIPHER_PADDING_ZEROS)
+    case POLARSSL_PADDING_ZEROS:
+        ctx->add_padding = add_zeros_padding;
+        ctx->get_padding = get_zeros_padding;
+        break;
+#endif
+    case POLARSSL_PADDING_NONE:
+        ctx->add_padding = NULL;
+        ctx->get_padding = get_no_padding;
+        break;
+
+    default:
+        return POLARSSL_ERR_CIPHER_FEATURE_UNAVAILABLE;
+    }
+
+    return 0;
+}
+#endif /* POLARSSL_CIPHER_MODE_WITH_PADDING */
+
+#if defined(POLARSSL_CIPHER_MODE_AEAD)
+int cipher_write_tag( cipher_context_t *ctx,
+                      unsigned char *tag, size_t tag_len )
+{
+    if( NULL == ctx || NULL == ctx->cipher_info || NULL == tag )
+        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+
+    if( POLARSSL_ENCRYPT != ctx->operation )
+        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+
+#if defined(POLARSSL_GCM_C)
+    if( POLARSSL_MODE_GCM == ctx->cipher_info->mode )
+        return gcm_finish( (gcm_context *) ctx->cipher_ctx, tag, tag_len );
+#endif
+
+    return 0;
+}
+
+int cipher_check_tag( cipher_context_t *ctx,
+                      const unsigned char *tag, size_t tag_len )
+{
+    int ret;
+
+    if( NULL == ctx || NULL == ctx->cipher_info ||
+        POLARSSL_DECRYPT != ctx->operation )
+    {
+        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+    }
+
+#if defined(POLARSSL_GCM_C)
+    if( POLARSSL_MODE_GCM == ctx->cipher_info->mode )
+    {
+        unsigned char check_tag[16];
+        size_t i;
+        int diff;
+
+        if( tag_len > sizeof( check_tag ) )
+            return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
+
+        if( 0 != ( ret = gcm_finish( (gcm_context *) ctx->cipher_ctx,
+                                     check_tag, tag_len ) ) )
+        {
+            return( ret );
+        }
+
+        /* Check the tag in "constant-time" */
+        for( diff = 0, i = 0; i < tag_len; i++ )
+            diff |= tag[i] ^ check_tag[i];
+
+        if( diff != 0 )
+            return( POLARSSL_ERR_CIPHER_AUTH_FAILED );
+
+        return( 0 );
+    }
+#endif /* POLARSSL_GCM_C */
+
+    return( 0 );
+}
+#endif /* POLARSSL_CIPHER_MODE_AEAD */
+
+#if defined(POLARSSL_SELF_TEST)
+
+/*
+ * Checkup routine
+ */
+int cipher_self_test( int verbose )
+{
+    ((void) verbose);
+
+    return( 0 );
+}
+
+#endif /* POLARSSL_SELF_TEST */
+
+#endif /* POLARSSL_CIPHER_C */
+
+