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Simplify CTR code

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This commit is contained in:
Andrew Ayer
2014-07-07 22:52:12 -07:00
parent 8de40f40b3
commit 23ff272f7d
2 changed files with 18 additions and 16 deletions
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27
crypto.cpp
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@@ -32,32 +32,33 @@
#include "util.hpp"
#include <cstring>
Aes_ctr_encryptor::Aes_ctr_encryptor (const unsigned char* raw_key, const unsigned char* arg_nonce)
Aes_ctr_encryptor::Aes_ctr_encryptor (const unsigned char* raw_key, const unsigned char* nonce)
: ecb(raw_key)
{
std::memcpy(nonce, arg_nonce, NONCE_LEN);
// Set first 12 bytes of the CTR value to the nonce.
// This stays the same for the entirety of this object's lifetime.
std::memcpy(ctr_value, nonce, NONCE_LEN);
byte_counter = 0;
std::memset(otp, '\0', sizeof(otp));
}
Aes_ctr_encryptor::~Aes_ctr_encryptor ()
{
std::memset(pad, '\0', BLOCK_LEN);
}
void Aes_ctr_encryptor::process (const unsigned char* in, unsigned char* out, size_t len)
{
for (size_t i = 0; i < len; ++i) {
if (byte_counter % BLOCK_LEN == 0) {
unsigned char ctr[BLOCK_LEN];
// Set last 4 bytes of CTR to the (big-endian) block number (sequentially increasing with each block)
store_be32(ctr_value + NONCE_LEN, byte_counter / BLOCK_LEN);
// First 12 bytes of CTR: nonce
std::memcpy(ctr, nonce, NONCE_LEN);
// Last 4 bytes of CTR: block number (sequentially increasing with each block) (big endian)
store_be32(ctr + NONCE_LEN, byte_counter / BLOCK_LEN);
// Generate a new OTP
ecb.encrypt(ctr, otp);
// Generate a new pad
ecb.encrypt(ctr_value, pad);
}
// encrypt one byte
out[i] = in[i] ^ otp[byte_counter++ % BLOCK_LEN];
out[i] = in[i] ^ pad[byte_counter++ % BLOCK_LEN];
if (byte_counter == 0) {
throw Crypto_error("Aes_ctr_encryptor::process", "Too much data to encrypt securely");