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/*
* Cryptobox Message Routines
* (C) 2009 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/cryptobox.h>
#include <botan/filters.h>
#include <botan/pipe.h>
#include <botan/lookup.h>
#include <botan/sha2_64.h>
#include <botan/hmac.h>
#include <botan/pbkdf2.h>
#include <botan/pem.h>
#include <botan/get_byte.h>
#include <botan/mem_ops.h>
namespace Botan {
namespace CryptoBox {
namespace {
/*
First 24 bits of SHA-256("Botan Cryptobox"), followed by 8 0 bits
for later use as flags, etc if needed
*/
const u32bit CRYPTOBOX_VERSION_CODE = 0xEFC22400;
const u32bit VERSION_CODE_LEN = 4;
const u32bit CIPHER_KEY_LEN = 32;
const u32bit CIPHER_IV_LEN = 16;
const u32bit MAC_KEY_LEN = 32;
const u32bit MAC_OUTPUT_LEN = 20;
const u32bit PBKDF_SALT_LEN = 10;
const u32bit PBKDF_ITERATIONS = 8 * 1024;
const u32bit PBKDF_OUTPUT_LEN = CIPHER_KEY_LEN + CIPHER_IV_LEN + MAC_KEY_LEN;
}
std::string encrypt(const byte input[], u32bit input_len,
const std::string& passphrase,
RandomNumberGenerator& rng)
{
SecureVector<byte> pbkdf_salt(PBKDF_SALT_LEN);
rng.randomize(&pbkdf_salt[0], pbkdf_salt.size());
PKCS5_PBKDF2 pbkdf(new HMAC(new SHA_512));
OctetString master_key = pbkdf.derive_key(
PBKDF_OUTPUT_LEN,
passphrase,
&pbkdf_salt[0],
pbkdf_salt.size(),
PBKDF_ITERATIONS);
const byte* mk = master_key.begin();
SymmetricKey cipher_key(&mk[0], CIPHER_KEY_LEN);
SymmetricKey mac_key(&mk[CIPHER_KEY_LEN], MAC_KEY_LEN);
InitializationVector iv(&mk[CIPHER_KEY_LEN + MAC_KEY_LEN], CIPHER_IV_LEN);
Pipe pipe(get_cipher("Serpent/CTR-BE", cipher_key, iv, ENCRYPTION),
new Fork(
0,
new MAC_Filter(new HMAC(new SHA_512),
mac_key, MAC_OUTPUT_LEN)));
pipe.process_msg(input, input_len);
/*
Output format is:
version # (4 bytes)
salt (10 bytes)
mac (20 bytes)
ciphertext
*/
const u32bit ciphertext_len = pipe.remaining(0);
SecureVector<byte> out_buf(VERSION_CODE_LEN +
PBKDF_SALT_LEN +
MAC_OUTPUT_LEN +
ciphertext_len);
for(u32bit i = 0; i != VERSION_CODE_LEN; ++i)
out_buf[i] = get_byte(i, CRYPTOBOX_VERSION_CODE);
copy_mem(&out_buf[VERSION_CODE_LEN], &pbkdf_salt[0], PBKDF_SALT_LEN);
pipe.read(&out_buf[VERSION_CODE_LEN + PBKDF_SALT_LEN], MAC_OUTPUT_LEN, 1);
pipe.read(&out_buf[VERSION_CODE_LEN + PBKDF_SALT_LEN + MAC_OUTPUT_LEN],
ciphertext_len, 0);
return PEM_Code::encode(out_buf, "BOTAN CRYPTOBOX MESSAGE");
}
std::string decrypt(const byte input[], u32bit input_len,
const std::string& passphrase)
{
DataSource_Memory input_src(input, input_len);
SecureVector<byte> ciphertext =
PEM_Code::decode_check_label(input_src,
"BOTAN CRYPTOBOX MESSAGE");
if(ciphertext.size() < (VERSION_CODE_LEN + PBKDF_SALT_LEN + MAC_OUTPUT_LEN))
throw Decoding_Error("Invalid CryptoBox input");
for(u32bit i = 0; i != VERSION_CODE_LEN; ++i)
if(ciphertext[i] != get_byte(i, CRYPTOBOX_VERSION_CODE))
throw Decoding_Error("Bad CryptoBox version");
const byte* pbkdf_salt = &ciphertext[VERSION_CODE_LEN];
PKCS5_PBKDF2 pbkdf(new HMAC(new SHA_512));
OctetString master_key = pbkdf.derive_key(
PBKDF_OUTPUT_LEN,
passphrase,
pbkdf_salt,
PBKDF_SALT_LEN,
PBKDF_ITERATIONS);
const byte* mk = master_key.begin();
SymmetricKey cipher_key(&mk[0], CIPHER_KEY_LEN);
SymmetricKey mac_key(&mk[CIPHER_KEY_LEN], MAC_KEY_LEN);
InitializationVector iv(&mk[CIPHER_KEY_LEN + MAC_KEY_LEN], CIPHER_IV_LEN);
Pipe pipe(new Fork(
get_cipher("Serpent/CTR-BE", cipher_key, iv, DECRYPTION),
new MAC_Filter(new HMAC(new SHA_512),
mac_key, MAC_OUTPUT_LEN)));
const u32bit ciphertext_offset =
VERSION_CODE_LEN + PBKDF_SALT_LEN + MAC_OUTPUT_LEN;
pipe.process_msg(&ciphertext[ciphertext_offset],
ciphertext.size() - ciphertext_offset);
byte computed_mac[MAC_OUTPUT_LEN];
pipe.read(computed_mac, MAC_OUTPUT_LEN, 1);
if(!same_mem(computed_mac,
&ciphertext[VERSION_CODE_LEN + PBKDF_SALT_LEN],
MAC_OUTPUT_LEN))
throw Decoding_Error("CryptoBox integrity failure");
return pipe.read_all_as_string(0);
}
std::string decrypt(const std::string& input,
const std::string& passphrase)
{
return decrypt(reinterpret_cast<const byte*>(&input[0]),
input.size(),
passphrase);
}
}
}
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