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/*
* Copyright 2020-2021 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the Apache License 2.0 (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
/*
* Helper functions for 128 bit CBC CTS ciphers (Currently AES and Camellia).
*
* The function dispatch tables are embedded into cipher_aes.c
* and cipher_camellia.c using cipher_aes_cts.inc and cipher_camellia_cts.inc
*/
/*
* Refer to SP800-38A-Addendum
*
* Ciphertext stealing encrypts plaintext using a block cipher, without padding
* the message to a multiple of the block size, so the ciphertext is the same
* size as the plaintext.
* It does this by altering processing of the last two blocks of the message.
* The processing of all but the last two blocks is unchanged, but a portion of
* the second-last block's ciphertext is "stolen" to pad the last plaintext
* block. The padded final block is then encrypted as usual.
* The final ciphertext for the last two blocks, consists of the partial block
* (with the "stolen" portion omitted) plus the full final block,
* which are the same size as the original plaintext.
* Decryption requires decrypting the final block first, then restoring the
* stolen ciphertext to the partial block, which can then be decrypted as usual.
* AES_CBC_CTS has 3 variants:
* (1) CS1 The NIST variant.
* If the length is a multiple of the blocksize it is the same as CBC mode.
* otherwise it produces C1||C2||(C(n-1))*||Cn.
* Where C(n-1)* is a partial block.
* (2) CS2
* If the length is a multiple of the blocksize it is the same as CBC mode.
* otherwise it produces C1||C2||Cn||(C(n-1))*.
* Where C(n-1)* is a partial block.
* (3) CS3 The Kerberos5 variant.
* Produces C1||C2||Cn||(C(n-1))* regardless of the length.
* If the length is a multiple of the blocksize it looks similar to CBC mode
* with the last 2 blocks swapped.
* Otherwise it is the same as CS2.
*/
#include "e_os.h" /* strcasecmp */
#include <openssl/core_names.h>
#include "prov/ciphercommon.h"
#include "internal/nelem.h"
#include "cipher_cts.h"
/* The value assigned to 0 is the default */
#define CTS_CS1 0
#define CTS_CS2 1
#define CTS_CS3 2
#define CTS_BLOCK_SIZE 16
typedef union {
size_t align;
unsigned char c[CTS_BLOCK_SIZE];
} aligned_16bytes;
typedef struct cts_mode_name2id_st {
unsigned int id;
const char *name;
} CTS_MODE_NAME2ID;
static CTS_MODE_NAME2ID cts_modes[] =
{
{ CTS_CS1, OSSL_CIPHER_CTS_MODE_CS1 },
{ CTS_CS2, OSSL_CIPHER_CTS_MODE_CS2 },
{ CTS_CS3, OSSL_CIPHER_CTS_MODE_CS3 },
};
const char *ossl_cipher_cbc_cts_mode_id2name(unsigned int id)
{
size_t i;
for (i = 0; i < OSSL_NELEM(cts_modes); ++i) {
if (cts_modes[i].id == id)
return cts_modes[i].name;
}
return NULL;
}
int ossl_cipher_cbc_cts_mode_name2id(const char *name)
{
size_t i;
for (i = 0; i < OSSL_NELEM(cts_modes); ++i) {
if (strcasecmp(name, cts_modes[i].name) == 0)
return (int)cts_modes[i].id;
}
return -1;
}
static size_t cts128_cs1_encrypt(PROV_CIPHER_CTX *ctx, const unsigned char *in,
unsigned char *out, size_t len)
{
aligned_16bytes tmp_in;
size_t residue;
residue = len % CTS_BLOCK_SIZE;
len -= residue;
if (!ctx->hw->cipher(ctx, out, in, len))
return 0;
if (residue == 0)
return len;
in += len;
out += len;
memset(tmp_in.c, 0, sizeof(tmp_in));
memcpy(tmp_in.c, in, residue);
if (!ctx->hw->cipher(ctx, out - CTS_BLOCK_SIZE + residue, tmp_in.c,
CTS_BLOCK_SIZE))
return 0;
return len + residue;
}
static void do_xor(const unsigned char *in1, const unsigned char *in2,
size_t len, unsigned char *out)
{
size_t i;
for (i = 0; i < len; ++i)
out[i] = in1[i] ^ in2[i];
}
static size_t cts128_cs1_decrypt(PROV_CIPHER_CTX *ctx, const unsigned char *in,
unsigned char *out, size_t len)
{
aligned_16bytes mid_iv, ct_mid, pt_last;
size_t residue;
residue = len % CTS_BLOCK_SIZE;
if (residue == 0) {
/* If there are no partial blocks then it is the same as CBC mode */
if (!ctx->hw->cipher(ctx, out, in, len))
return 0;
return len;
}
/* Process blocks at the start - but leave the last 2 blocks */
len -= CTS_BLOCK_SIZE + residue;
if (len > 0) {
if (!ctx->hw->cipher(ctx, out, in, len))
return 0;
in += len;
out += len;
}
/* Save the iv that will be used by the second last block */
memcpy(mid_iv.c, ctx->iv, CTS_BLOCK_SIZE);
/* Decrypt the last block first using an iv of zero */
memset(ctx->iv, 0, CTS_BLOCK_SIZE);
if (!ctx->hw->cipher(ctx, pt_last.c, in + residue, CTS_BLOCK_SIZE))
return 0;
/*
* Rebuild the ciphertext of the second last block as a combination of
* the decrypted last block + replace the start with the ciphertext bytes
* of the partial second last block.
*/
memcpy(ct_mid.c, in, residue);
memcpy(ct_mid.c + residue, pt_last.c + residue, CTS_BLOCK_SIZE - residue);
/*
* Restore the last partial ciphertext block.
* Now that we have the cipher text of the second last block, apply
* that to the partial plaintext end block. We have already decrypted the
* block using an IV of zero. For decryption the IV is just XORed after
* doing an Cipher CBC block - so just XOR in the cipher text.
*/
do_xor(ct_mid.c, pt_last.c, residue, out + CTS_BLOCK_SIZE);
/* Restore the iv needed by the second last block */
memcpy(ctx->iv, mid_iv.c, CTS_BLOCK_SIZE);
/*
* Decrypt the second last plaintext block now that we have rebuilt the
* ciphertext.
*/
if (!ctx->hw->cipher(ctx, out, ct_mid.c, CTS_BLOCK_SIZE))
return 0;
return len + CTS_BLOCK_SIZE + residue;
}
static size_t cts128_cs3_encrypt(PROV_CIPHER_CTX *ctx, const unsigned char *in,
unsigned char *out, size_t len)
{
aligned_16bytes tmp_in;
size_t residue;
if (len < CTS_BLOCK_SIZE) /* CS3 requires at least one block */
return 0;
/* If we only have one block then just process the aligned block */
if (len == CTS_BLOCK_SIZE)
return ctx->hw->cipher(ctx, out, in, len) ? len : 0;
residue = len % CTS_BLOCK_SIZE;
if (residue == 0)
residue = CTS_BLOCK_SIZE;
len -= residue;
if (!ctx->hw->cipher(ctx, out, in, len))
return 0;
in += len;
out += len;
memset(tmp_in.c, 0, sizeof(tmp_in));
memcpy(tmp_in.c, in, residue);
memcpy(out, out - CTS_BLOCK_SIZE, residue);
if (!ctx->hw->cipher(ctx, out - CTS_BLOCK_SIZE, tmp_in.c, CTS_BLOCK_SIZE))
return 0;
return len + residue;
}
/*
* Note:
* The cipher text (in) is of the form C(0), C(1), ., C(n), C(n-1)* where
* C(n) is a full block and C(n-1)* can be a partial block
* (but could be a full block).
* This means that the output plaintext (out) needs to swap the plaintext of
* the last two decoded ciphertext blocks.
*/
static size_t cts128_cs3_decrypt(PROV_CIPHER_CTX *ctx, const unsigned char *in,
unsigned char *out, size_t len)
{
aligned_16bytes mid_iv, ct_mid, pt_last;
size_t residue;
if (len < CTS_BLOCK_SIZE) /* CS3 requires at least one block */
return 0;
/* If we only have one block then just process the aligned block */
if (len == CTS_BLOCK_SIZE)
return ctx->hw->cipher(ctx, out, in, len) ? len : 0;
/* Process blocks at the start - but leave the last 2 blocks */
residue = len % CTS_BLOCK_SIZE;
if (residue == 0)
residue = CTS_BLOCK_SIZE;
len -= CTS_BLOCK_SIZE + residue;
if (len > 0) {
if (!ctx->hw->cipher(ctx, out, in, len))
return 0;
in += len;
out += len;
}
/* Save the iv that will be used by the second last block */
memcpy(mid_iv.c, ctx->iv, CTS_BLOCK_SIZE);
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