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pcbc.hpp
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pcbc.hpp
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#include <openssl/evp.h>
#include <string.h>
#include "./types.h"
// define in parens, so it doesn't cause @bugs with operations order
// (256 / 8)
// all aes ciphers have block size 16
const auto ECB_CIPHER = EVP_aes_256_ecb();
const auto BLOCK_SIZE = EVP_CIPHER_get_block_size(ECB_CIPHER);
const auto XOR_OP_SIZE = BLOCK_SIZE / sizeof(size_t);
#define IV_SIZE BLOCK_SIZE
// faster xor with size_t?
// compiler should optimize it to use 128/256 bit operations doe
// dest = b0 ^ b1
void xor_block(size_t *b0, size_t *b1, size_t *dest)
{
for (size_t i = 0; i < XOR_OP_SIZE; i += 1)
{
dest[i] = b0[i] ^ b1[i];
}
}
void pcbc_encrypt_round(EVP_CIPHER_CTX *ctx, const byte *in, byte *out, byte *op)
{
int encrypted_size;
// plaintext ^ operation (= iv OR prev_plaintext & prev_ciphertext)
xor_block(
(size_t *)in,
(size_t *)op,
(size_t *)op);
// encrypt
if (!EVP_EncryptUpdate(
ctx,
out,
&encrypted_size,
op,
BLOCK_SIZE))
handle_ossl_error();
// prepare next operation = plaintext ^ ciphertext
xor_block(
(size_t *)in,
(size_t *)out,
(size_t *)op);
// printf("[PCBC] Encrypted len = %d\n", encrypted_size);
}
void encrypt_aes256_pcbc(const byte *plaintext, const size_t plaintext_size, const byte *key, byte *iv, byte *&ciphertext, size_t &ciphertext_size)
{
// iv OR ciphertext ^ plaintext
byte operation_buffer[BLOCK_SIZE];
// clear iv to 0
// memset(operation_buffer, 0, BLOCK_SIZE);
memcpy(operation_buffer, iv, BLOCK_SIZE);
size_t padding_size = BLOCK_SIZE - plaintext_size % BLOCK_SIZE;
ciphertext_size = plaintext_size + padding_size;
ciphertext = new byte[ciphertext_size];
EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
if (ctx == NULL)
handle_ossl_error();
if (!EVP_EncryptInit(ctx, ECB_CIPHER, key, NULL))
handle_ossl_error();
// @note !!! it's required to disable padding
if (!EVP_CIPHER_CTX_set_padding(ctx, 0))
handle_ossl_error();
// encrypt full blocks
for (size_t b = 0; b + BLOCK_SIZE <= plaintext_size; b += BLOCK_SIZE)
{
pcbc_encrypt_round(
ctx,
plaintext + b,
ciphertext + b,
operation_buffer);
}
/// encrypt last block
// copy remaining bytes
// use end of ciphertext to store padded plaintext
// temp store for padded final plaintext block
byte *last_ciphertext_block = ciphertext + ciphertext_size - BLOCK_SIZE;
memcpy(
last_ciphertext_block,
plaintext + ciphertext_size - BLOCK_SIZE,
BLOCK_SIZE - padding_size);
// set padding
memset(
last_ciphertext_block + BLOCK_SIZE - padding_size,
padding_size,
padding_size);
pcbc_encrypt_round(
ctx,
last_ciphertext_block,
last_ciphertext_block,
operation_buffer);
EVP_CIPHER_CTX_free(ctx);
}
void pcbc_decrypt_round(EVP_CIPHER_CTX *ctx, const byte *in, byte *out, byte *op)
{
int decrypted_size;
if (!EVP_DecryptUpdate(ctx, out, &decrypted_size, in, BLOCK_SIZE))
handle_ossl_error();
// plaintext = decrypted ^ op (= iv OR prev_ciphertext ^ prev_plaintext)
xor_block(
(size_t *)out,
(size_t *)op,
(size_t *)out);
// update op = ciphertext ^ plaintext
xor_block(
(size_t *)in,
(size_t *)out,
(size_t *)op);
// printf("[PCBC] Decrypted len = %d\n", decrypted_size);
}
void decrypt_aes256_pcbc(const byte *ciphertext, const size_t ciphertext_size, const byte *key, byte *iv, byte *&plaintext, size_t &plaintext_size)
{
byte operation_buffer[BLOCK_SIZE];
// memset(operation_buffer, 0, BLOCK_SIZE);
memcpy(operation_buffer, iv, BLOCK_SIZE);
plaintext = new byte[ciphertext_size];
EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
if (ctx == NULL)
handle_ossl_error();
if (!EVP_DecryptInit(ctx, ECB_CIPHER, key, NULL))
handle_ossl_error();
if (!EVP_CIPHER_CTX_set_padding(ctx, 0))
handle_ossl_error();
for (size_t b = 0; b < ciphertext_size; b += BLOCK_SIZE)
{
pcbc_decrypt_round(
ctx,
ciphertext + b,
plaintext + b,
operation_buffer);
}
size_t padding_size = plaintext[ciphertext_size - 1];
// @note sometimes incorrect password may lead to incorrect decryption and thus
// extremely big plaintext_size values, when padding_size turns out to be bigger
// than ciphertext size (overflow)
if (padding_size > BLOCK_SIZE)
{
print_error("Integrity is broken or password is incorrect!");
abort();
}
plaintext_size = ciphertext_size - padding_size;
EVP_CIPHER_CTX_free(ctx);
}