RFC 5649 support.
authorDr. Stephen Henson <steve@openssl.org>
Fri, 18 Jul 2014 12:52:03 +0000 (13:52 +0100)
committerDr. Stephen Henson <steve@openssl.org>
Fri, 18 Jul 2014 20:37:13 +0000 (21:37 +0100)
Add support for RFC5649 key wrapping with padding.

Add RFC5649 tests to evptests.txt

Based on PR#3434 contribution by Petr Spacek <pspacek@redhat.com>.

EVP support and minor changes added by Stephen Henson.

Doxygen comment block updates by Tim Hudson.

Reviewed-by: Tim Hudson <tjh@openssl.org>
crypto/evp/c_allc.c
crypto/evp/e_aes.c
crypto/evp/evp.h
crypto/evp/evptests.txt
crypto/modes/modes.h
crypto/modes/wrap128.c

index 4cfe5a9..a714f12 100644 (file)
@@ -175,6 +175,7 @@ void OpenSSL_add_all_ciphers(void)
        EVP_add_cipher(EVP_aes_128_xts());
        EVP_add_cipher(EVP_aes_128_ccm());
        EVP_add_cipher(EVP_aes_128_wrap());
+       EVP_add_cipher(EVP_aes_128_wrap_pad());
        EVP_add_cipher_alias(SN_aes_128_cbc,"AES128");
        EVP_add_cipher_alias(SN_aes_128_cbc,"aes128");
        EVP_add_cipher(EVP_aes_192_ecb());
@@ -187,6 +188,7 @@ void OpenSSL_add_all_ciphers(void)
        EVP_add_cipher(EVP_aes_192_gcm());
        EVP_add_cipher(EVP_aes_192_ccm());
        EVP_add_cipher(EVP_aes_192_wrap());
+       EVP_add_cipher(EVP_aes_192_wrap_pad());
        EVP_add_cipher_alias(SN_aes_192_cbc,"AES192");
        EVP_add_cipher_alias(SN_aes_192_cbc,"aes192");
        EVP_add_cipher(EVP_aes_256_ecb());
@@ -200,6 +202,7 @@ void OpenSSL_add_all_ciphers(void)
        EVP_add_cipher(EVP_aes_256_xts());
        EVP_add_cipher(EVP_aes_256_ccm());
        EVP_add_cipher(EVP_aes_256_wrap());
+       EVP_add_cipher(EVP_aes_256_wrap_pad());
        EVP_add_cipher_alias(SN_aes_256_cbc,"AES256");
        EVP_add_cipher_alias(SN_aes_256_cbc,"aes256");
 #if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
index 3501066..89178bc 100644 (file)
@@ -1,5 +1,5 @@
 /* ====================================================================
- * Copyright (c) 2001-2011 The OpenSSL Project.  All rights reserved.
+ * Copyright (c) 2001-2014 The OpenSSL Project.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -2086,7 +2086,7 @@ static int aes_wrap_init_key(EVP_CIPHER_CTX *ctx, const unsigned char *key,
                }
        if (iv)
                {
-               memcpy(ctx->iv, iv, 8);
+               memcpy(ctx->iv, iv, EVP_CIPHER_CTX_iv_length(ctx));
                wctx->iv = ctx->iv;
                }
        return 1;
@@ -2097,27 +2097,62 @@ static int aes_wrap_cipher(EVP_CIPHER_CTX *ctx, unsigned char *out,
        {
        EVP_AES_WRAP_CTX *wctx = ctx->cipher_data;
        size_t rv;
+       /* AES wrap with padding has IV length of 4, without padding 8 */
+       int pad = EVP_CIPHER_CTX_iv_length(ctx) == 4;
+       /* No final operation so always return zero length */
        if (!in)
                return 0;
-       if (inlen % 8)
+       /* Input length must always be non-zero */
+       if (!inlen)
                return -1;
-       if (ctx->encrypt && inlen < 8)
+       /* If decrypting need at least 16 bytes and multiple of 8 */
+       if (!ctx->encrypt && (inlen < 16 || inlen & 0x7))
                return -1;
-       if (!ctx->encrypt && inlen < 16)
+       /* If not padding input must be multiple of 8 */
+       if (!pad && inlen & 0x7)
                return -1;
        if (!out)
                {
                if (ctx->encrypt)
+                       {
+                       /* If padding round up to multiple of 8 */
+                       if (pad)
+                               inlen = (inlen + 7)/8 * 8;
+                       /* 8 byte prefix */
                        return inlen + 8;
+                       }
                else
+                       {
+                       /* If not padding output will be exactly 8 bytes
+                        * smaller than input. If padding it will be at
+                        * least 8 bytes smaller but we don't know how
+                        * much.
+                        */
                        return inlen - 8;
+                       }
                }
-       if (ctx->encrypt)
-               rv = CRYPTO_128_wrap(&wctx->ks.ks, wctx->iv, out, in, inlen,
+       if (pad)
+               {
+               if (ctx->encrypt)
+                       rv = CRYPTO_128_wrap_pad(&wctx->ks.ks, wctx->iv,
+                                               out, in, inlen,
                                                (block128_f)AES_encrypt);
+               else
+                       rv = CRYPTO_128_unwrap_pad(&wctx->ks.ks, wctx->iv,
+                                               out, in, inlen,
+                                               (block128_f)AES_decrypt);
+               }
        else
-               rv = CRYPTO_128_unwrap(&wctx->ks.ks, wctx->iv, out, in, inlen,
+               {
+               if (ctx->encrypt)
+                       rv = CRYPTO_128_wrap(&wctx->ks.ks, wctx->iv,
+                                               out, in, inlen,
+                                               (block128_f)AES_encrypt);
+               else
+                       rv = CRYPTO_128_unwrap(&wctx->ks.ks, wctx->iv,
+                                               out, in, inlen,
                                                (block128_f)AES_decrypt);
+               }
        return rv ? (int)rv : -1;
        }
 
@@ -2129,7 +2164,7 @@ static const EVP_CIPHER aes_128_wrap = {
        NID_id_aes128_wrap,
        8, 16, 8, WRAP_FLAGS,
        aes_wrap_init_key, aes_wrap_cipher,
-       NULL,   
+       NULL,
        sizeof(EVP_AES_WRAP_CTX),
        NULL,NULL,NULL,NULL };
 
@@ -2142,7 +2177,7 @@ static const EVP_CIPHER aes_192_wrap = {
        NID_id_aes192_wrap,
        8, 24, 8, WRAP_FLAGS,
        aes_wrap_init_key, aes_wrap_cipher,
-       NULL,   
+       NULL,
        sizeof(EVP_AES_WRAP_CTX),
        NULL,NULL,NULL,NULL };
 
@@ -2155,7 +2190,7 @@ static const EVP_CIPHER aes_256_wrap = {
        NID_id_aes256_wrap,
        8, 32, 8, WRAP_FLAGS,
        aes_wrap_init_key, aes_wrap_cipher,
-       NULL,   
+       NULL,
        sizeof(EVP_AES_WRAP_CTX),
        NULL,NULL,NULL,NULL };
 
@@ -2164,4 +2199,43 @@ const EVP_CIPHER *EVP_aes_256_wrap(void)
        return &aes_256_wrap;
        }
 
+static const EVP_CIPHER aes_128_wrap_pad = {
+       NID_id_aes128_wrap_pad,
+       8, 16, 4, WRAP_FLAGS,
+       aes_wrap_init_key, aes_wrap_cipher,
+       NULL,
+       sizeof(EVP_AES_WRAP_CTX),
+       NULL,NULL,NULL,NULL };
+
+const EVP_CIPHER *EVP_aes_128_wrap_pad(void)
+       {
+       return &aes_128_wrap_pad;
+       }
+
+static const EVP_CIPHER aes_192_wrap_pad = {
+       NID_id_aes192_wrap_pad,
+       8, 24, 4, WRAP_FLAGS,
+       aes_wrap_init_key, aes_wrap_cipher,
+       NULL,
+       sizeof(EVP_AES_WRAP_CTX),
+       NULL,NULL,NULL,NULL };
+
+const EVP_CIPHER *EVP_aes_192_wrap_pad(void)
+       {
+       return &aes_192_wrap_pad;
+       }
+
+static const EVP_CIPHER aes_256_wrap_pad = {
+       NID_id_aes256_wrap_pad,
+       8, 32, 4, WRAP_FLAGS,
+       aes_wrap_init_key, aes_wrap_cipher,
+       NULL,
+       sizeof(EVP_AES_WRAP_CTX),
+       NULL,NULL,NULL,NULL };
+
+const EVP_CIPHER *EVP_aes_256_wrap_pad(void)
+       {
+       return &aes_256_wrap_pad;
+       }
+
 #endif
index ea92aa2..bafe339 100644 (file)
@@ -849,6 +849,7 @@ const EVP_CIPHER *EVP_aes_128_ccm(void);
 const EVP_CIPHER *EVP_aes_128_gcm(void);
 const EVP_CIPHER *EVP_aes_128_xts(void);
 const EVP_CIPHER *EVP_aes_128_wrap(void);
+const EVP_CIPHER *EVP_aes_128_wrap_pad(void);
 const EVP_CIPHER *EVP_aes_192_ecb(void);
 const EVP_CIPHER *EVP_aes_192_cbc(void);
 const EVP_CIPHER *EVP_aes_192_cfb1(void);
@@ -860,6 +861,7 @@ const EVP_CIPHER *EVP_aes_192_ctr(void);
 const EVP_CIPHER *EVP_aes_192_ccm(void);
 const EVP_CIPHER *EVP_aes_192_gcm(void);
 const EVP_CIPHER *EVP_aes_192_wrap(void);
+const EVP_CIPHER *EVP_aes_192_wrap_pad(void);
 const EVP_CIPHER *EVP_aes_256_ecb(void);
 const EVP_CIPHER *EVP_aes_256_cbc(void);
 const EVP_CIPHER *EVP_aes_256_cfb1(void);
@@ -872,6 +874,7 @@ const EVP_CIPHER *EVP_aes_256_ccm(void);
 const EVP_CIPHER *EVP_aes_256_gcm(void);
 const EVP_CIPHER *EVP_aes_256_xts(void);
 const EVP_CIPHER *EVP_aes_256_wrap(void);
+const EVP_CIPHER *EVP_aes_256_wrap_pad(void);
 # if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
 const EVP_CIPHER *EVP_aes_128_cbc_hmac_sha1(void);
 const EVP_CIPHER *EVP_aes_256_cbc_hmac_sha1(void);
index 4744fef..42eb42e 100644 (file)
@@ -401,3 +401,7 @@ id-aes256-wrap:000102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F:
 id-aes192-wrap:000102030405060708090A0B0C0D0E0F1011121314151617::00112233445566778899AABBCCDDEEFF0001020304050607:031D33264E15D33268F24EC260743EDCE1C6C7DDEE725A936BA814915C6762D2
 id-aes256-wrap:000102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F::00112233445566778899AABBCCDDEEFF0001020304050607:A8F9BC1612C68B3FF6E6F4FBE30E71E4769C8B80A32CB8958CD5D17D6B254DA1
 id-aes256-wrap:000102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F::00112233445566778899AABBCCDDEEFF000102030405060708090A0B0C0D0E0F:28C9F404C4B810F4CBCCB35CFB87F8263F5786E2D80ED326CBC7F0E71A99F43BFB988B9B7A02DD21
+# AES wrap tests from RFC5649
+id-aes192-wrap-pad:5840df6e29b02af1ab493b705bf16ea1ae8338f4dcc176a8::c37b7e6492584340bed12207808941155068f738:138bdeaa9b8fa7fc61f97742e72248ee5ae6ae5360d1ae6a5f54f373fa543b6a
+id-aes192-wrap-pad:5840df6e29b02af1ab493b705bf16ea1ae8338f4dcc176a8::466f7250617369:afbeb0f07dfbf5419200f2ccb50bb24f
+
index 9912550..50dc018 100644 (file)
@@ -141,3 +141,9 @@ size_t CRYPTO_128_wrap(void *key, const unsigned char *iv,
 size_t CRYPTO_128_unwrap(void *key, const unsigned char *iv,
                unsigned char *out,
                const unsigned char *in, size_t inlen, block128_f block);
+size_t CRYPTO_128_wrap_pad(void *key, const unsigned char *icv,
+               unsigned char *out,
+               const unsigned char *in, size_t inlen, block128_f block);
+size_t CRYPTO_128_unwrap_pad(void *key, const unsigned char *icv,
+               unsigned char *out,
+               const unsigned char *in, size_t inlen, block128_f block);
index c6c14cd..315fe8f 100644 (file)
@@ -1,6 +1,7 @@
 /* crypto/modes/wrap128.c */
 /* Written by Dr Stephen N Henson (steve@openssl.org) for the OpenSSL
  * project.
+ * Mode with padding contributed by Petr Spacek (pspacek@redhat.com).
  */
 /* ====================================================================
  * Copyright (c) 2013 The OpenSSL Project.  All rights reserved.
  * ====================================================================
  */
 
+/**  Beware!
+ *
+ *  Following wrapping modes were designed for AES but this implementation
+ *  allows you to use them for any 128 bit block cipher.
+ */
+
 #include "cryptlib.h"
 #include <openssl/modes.h>
 
+/** RFC 3394 section 2.2.3.1 Default Initial Value */
 static const unsigned char default_iv[] = {
   0xA6, 0xA6, 0xA6, 0xA6, 0xA6, 0xA6, 0xA6, 0xA6,
 };
-/* Input size limit: lower than maximum of standards but far larger than
- * anything that will be used in practice.
+
+/** RFC 5649 section 3 Alternative Initial Value 32-bit constant */
+static const unsigned char default_aiv[] = {
+  0xA6, 0x59, 0x59, 0xA6
+};
+
+/** Input size limit: lower than maximum of standards but far larger than
+ *  anything that will be used in practice.
  */
 #define CRYPTO128_WRAP_MAX (1UL << 31)
 
+/** Wrapping according to RFC 3394 section 2.2.1.
+ *
+ *  @param[in]  key    Key value. 
+ *  @param[in]  iv     IV value. Length = 8 bytes. NULL = use default_iv.
+ *  @param[in]  in     Plain text as n 64-bit blocks, n >= 2.
+ *  @param[in]  inlen  Length of in.
+ *  @param[out] out    Cipher text. Minimal buffer length = (inlen + 8) bytes.
+ *                     Input and output buffers can overlap if block function
+ *                     supports that.
+ *  @param[in]  block  Block processing function.
+ *  @return            0 if inlen does not consist of n 64-bit blocks, n >= 2.
+ *                     or if inlen > CRYPTO128_WRAP_MAX.
+ *                     Output length if wrapping succeeded.
+ */
 size_t CRYPTO_128_wrap(void *key, const unsigned char *iv,
                unsigned char *out,
                const unsigned char *in, size_t inlen, block128_f block)
        {
        unsigned char *A, B[16], *R;
        size_t i, j, t;
-       if ((inlen & 0x7) || (inlen < 8) || (inlen > CRYPTO128_WRAP_MAX))
+       if ((inlen & 0x7) || (inlen < 16) || (inlen > CRYPTO128_WRAP_MAX))
                return 0;
        A = B;
        t = 1;
-       memcpy(out + 8, in, inlen);
+       memmove(out + 8, in, inlen);
        if (!iv)
                iv = default_iv;
 
@@ -99,9 +127,26 @@ size_t CRYPTO_128_wrap(void *key, const unsigned char *iv,
        return inlen + 8;
        }
 
-size_t CRYPTO_128_unwrap(void *key, const unsigned char *iv,
-               unsigned char *out,
-               const unsigned char *in, size_t inlen, block128_f block)
+
+/** Unwrapping according to RFC 3394 section 2.2.2 steps 1-2.
+ *  IV check (step 3) is responsibility of the caller.
+ *
+ *  @param[in]  key    Key value. 
+ *  @param[out] iv     Unchecked IV value. Minimal buffer length = 8 bytes.
+ *  @param[out] out    Plain text without IV.
+ *                     Minimal buffer length = (inlen - 8) bytes.
+ *                     Input and output buffers can overlap if block function
+ *                     supports that.
+ *  @param[in]  in     Ciphertext text as n 64-bit blocks
+ *  @param[in]  inlen  Length of in.
+ *  @param[in]  block  Block processing function.
+ *  @return            0 if inlen is out of range [24, CRYPTO128_WRAP_MAX]
+ *                     or if inlen is not multiply of 8.
+ *                     Output length otherwise.
+ */
+static size_t crypto_128_unwrap_raw(void *key, unsigned char *iv,
+               unsigned char *out, const unsigned char *in,
+               size_t inlen, block128_f block)
        {
        unsigned char *A, B[16], *R;
        size_t i, j, t;
@@ -111,7 +156,7 @@ size_t CRYPTO_128_unwrap(void *key, const unsigned char *iv,
        A = B;
        t =  6 * (inlen >> 3);
        memcpy(A, in, 8);
-       memcpy(out, in + 8, inlen);
+       memmove(out, in + 8, inlen);
        for (j = 0; j < 6; j++)
                {
                R = out + inlen - 8;
@@ -129,12 +174,199 @@ size_t CRYPTO_128_unwrap(void *key, const unsigned char *iv,
                        memcpy(R, B + 8, 8);
                        }
                }
+       memcpy(iv, A, 8);
+       return inlen;
+       }
+
+/** Unwrapping according to RFC 3394 section 2.2.2 including IV check.
+ *  First block of plain text have to match supplied IV otherwise an error is
+ *  returned.
+ *
+ *  @param[in]  key    Key value. 
+ *  @param[out] iv     Unchecked IV value. Minimal buffer length = 8 bytes.
+ *  @param[out] out    Plain text without IV.
+ *                     Minimal buffer length = (inlen - 8) bytes.
+ *                     Input and output buffers can overlap if block function
+ *                     supports that.
+ *  @param[in]  in     Ciphertext text as n 64-bit blocks
+ *  @param[in]  inlen  Length of in.
+ *  @param[in]  block  Block processing function.
+ *  @return            0 if inlen is out of range [24, CRYPTO128_WRAP_MAX]
+ *                     or if inlen is not multiply of 8
+ *                     or if IV doesn't match expected value.
+ *                     Output length otherwise.
+ */
+size_t CRYPTO_128_unwrap(void *key, const unsigned char *iv,
+               unsigned char *out, const unsigned char *in, size_t inlen,
+               block128_f block)
+       {
+       size_t ret;
+       unsigned char got_iv[8];
+
+       ret = crypto_128_unwrap_raw(key, got_iv, out, in, inlen, block);
+       if (ret != inlen)
+               return ret;
+
        if (!iv)
                iv = default_iv;
-       if (memcmp(A, iv, 8))
+       if (CRYPTO_memcmp(out, iv, 8))
                {
                OPENSSL_cleanse(out, inlen);
                return 0;
                }
        return inlen;
        }
+
+/** Wrapping according to RFC 5649 section 4.1.
+ *
+ *  @param[in]  key    Key value. 
+ *  @param[in]  icv    (Non-standard) IV, 4 bytes. NULL = use default_aiv.
+ *  @param[out] out    Cipher text. Minimal buffer length = (inlen + 15) bytes.
+ *                     Input and output buffers can overlap if block function
+ *                     supports that.
+ *  @param[in]  in     Plain text as n 64-bit blocks, n >= 2.
+ *  @param[in]  inlen  Length of in.
+ *  @param[in]  block  Block processing function.
+ *  @return            0 if inlen is out of range [1, CRYPTO128_WRAP_MAX].
+ *                     Output length if wrapping succeeded.
+ */
+size_t CRYPTO_128_wrap_pad(void *key, const unsigned char *icv,
+               unsigned char *out,
+               const unsigned char *in, size_t inlen, block128_f block)
+       {
+       /* n: number of 64-bit blocks in the padded key data */
+       const size_t blocks_padded = (inlen + 8) / 8;
+       const size_t padded_len = blocks_padded * 8;
+       const size_t padding_len = padded_len - inlen;
+       /* RFC 5649 section 3: Alternative Initial Value */
+       unsigned char aiv[8];
+       int ret;
+
+       /* Section 1: use 32-bit fixed field for plaintext octet length */
+       if (inlen == 0 || inlen >= CRYPTO128_WRAP_MAX)
+               return 0;
+
+       /* Section 3: Alternative Initial Value */
+       if (!icv)
+               memcpy(aiv, default_aiv, 4);
+       else
+               memcpy(aiv, icv, 4); /* Standard doesn't mention this. */
+
+       aiv[4] = (inlen >> 24) & 0xFF;
+       aiv[5] = (inlen >> 16) & 0xFF;
+       aiv[6] = (inlen >> 8) & 0xFF;
+       aiv[7] = inlen & 0xFF;
+
+       if (padded_len == 8)
+               {
+               /* Section 4.1 - special case in step 2:
+                * If the padded plaintext contains exactly eight octets, then
+                * prepend the AIV and encrypt the resulting 128-bit block
+                * using AES in ECB mode. */
+               memmove(out + 8, in, inlen);
+               memcpy(out, aiv, 8);
+               memset(out + 8 + inlen, 0, padding_len);
+               block(out, out, key);
+               ret = 16; /* AIV + padded input */
+               }
+               else
+               {
+               memmove(out, in, inlen);
+               memset(out + inlen, 0, padding_len); /* Section 4.1 step 1 */
+               ret = CRYPTO_128_wrap(key, aiv, out, out, padded_len, block);
+               }
+
+       return ret;
+       }
+
+/** Unwrapping according to RFC 5649 section 4.2.
+ *
+ *  @param[in]  key    Key value. 
+ *  @param[in]  icv    (Non-standard) IV, 4 bytes. NULL = use default_aiv.
+ *  @param[out] out    Plain text. Minimal buffer length = inlen bytes.
+ *                     Input and output buffers can overlap if block function
+ *                     supports that.
+ *  @param[in]  in     Ciphertext text as n 64-bit blocks
+ *  @param[in]  inlen  Length of in.
+ *  @param[in]  block  Block processing function.
+ *  @return            0 if inlen is out of range [16, CRYPTO128_WRAP_MAX],
+ *                     or if inlen is not multiply of 8
+ *                     or if IV and message length indicator doesn't match.
+ *                     Output length if unwrapping succeeded and IV matches.
+ */
+size_t CRYPTO_128_unwrap_pad(void *key, const unsigned char *icv,
+               unsigned char *out,
+               const unsigned char *in, size_t inlen, block128_f block)
+       {
+       /* n: number of 64-bit blocks in the padded key data */
+       size_t n = inlen / 8 - 1;
+       size_t padded_len;
+       size_t padding_len;
+       size_t ptext_len;
+       /* RFC 5649 section 3: Alternative Initial Value */
+       unsigned char aiv[8];
+       static unsigned char zeros[8] = {0x0};
+       size_t ret;
+
+       /* Section 4.2: Cipher text length has to be (n+1) 64-bit blocks. */
+       if ((inlen & 0x7) != 0 || inlen < 16 || inlen >= CRYPTO128_WRAP_MAX)
+               return 0;
+
+       memmove(out, in, inlen);
+       if (inlen == 16)
+               {
+               /* Section 4.2 - special case in step 1:
+                * When n=1, the ciphertext contains exactly two 64-bit
+                * blocks and they are decrypted as a single AES
+                * block using AES in ECB mode:
+                * AIV | P[1] = DEC(K, C[0] | C[1])
+                */
+               block(out, out, key);
+               memcpy(aiv, out, 8);
+               /* Remove AIV */
+               memmove(out, out + 8, 8);
+               padded_len = 8;
+               }
+               else
+               {
+               padded_len = inlen - 8;
+               ret = crypto_128_unwrap_raw(key, aiv, out, out, inlen, block);
+               if (padded_len != ret)
+                       {
+                       OPENSSL_cleanse(out, inlen);
+                       return 0;
+                       }
+               }
+
+       /* Section 3: AIV checks: Check that MSB(32,A) = A65959A6.
+        * Optionally a user-supplied value can be used
+        * (even if standard doesn't mention this). */
+       if ((!icv && CRYPTO_memcmp(aiv, default_aiv, 4))
+               || (icv && CRYPTO_memcmp(aiv, icv, 4)))
+               {
+               OPENSSL_cleanse(out, inlen);
+               return 0;
+               }
+
+       /* Check that 8*(n-1) < LSB(32,AIV) <= 8*n.
+        * If so, let ptext_len = LSB(32,AIV). */
+
+       ptext_len = (aiv[4] << 24) | (aiv[5] << 16) | (aiv[6] << 8) | aiv[7];
+       if (8*(n-1) >= ptext_len || ptext_len > 8*n)
+               {
+               OPENSSL_cleanse(out, inlen);
+               return 0;
+               }
+
+       /* Check that the rightmost padding_len octets of the output data
+        * are zero. */
+       padding_len = padded_len - ptext_len;
+       if (CRYPTO_memcmp(out + ptext_len, zeros, padding_len) != 0)
+               {
+               OPENSSL_cleanse(out, inlen);
+               return 0;
+               }
+
+       /* Section 4.2 step 3: Remove padding */
+       return ptext_len;
+       }