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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/loadstor.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.begin(), pbkdf_salt.size());
PKCS5_PBKDF2 pbkdf(new HMAC(new SHA_512));
pbkdf.change_salt(pbkdf_salt.begin(), pbkdf_salt.size());
pbkdf.set_iterations(PBKDF_ITERATIONS);
OctetString mk = pbkdf.derive_key(PBKDF_OUTPUT_LEN, passphrase);
SymmetricKey cipher_key(mk.begin(), CIPHER_KEY_LEN);
SymmetricKey mac_key(mk.begin() + CIPHER_KEY_LEN, MAC_KEY_LEN);
InitializationVector iv(mk.begin() + 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
*/
u32bit ciphertext_len = pipe.remaining(0);
SecureVector<byte> out_buf;
for(u32bit i = 0; i != VERSION_CODE_LEN; ++i)
out_buf.append(get_byte(i, CRYPTOBOX_VERSION_CODE));
out_buf.append(pbkdf_salt.begin(), pbkdf_salt.size());
out_buf.grow_to(out_buf.size() + MAC_OUTPUT_LEN + ciphertext_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.begin(), out_buf.size(),
"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");
SecureVector<byte> pbkdf_salt(ciphertext + VERSION_CODE_LEN, PBKDF_SALT_LEN);
PKCS5_PBKDF2 pbkdf(new HMAC(new SHA_512));
pbkdf.change_salt(pbkdf_salt.begin(), pbkdf_salt.size());
pbkdf.set_iterations(PBKDF_ITERATIONS);
OctetString mk = pbkdf.derive_key(PBKDF_OUTPUT_LEN, passphrase);
SymmetricKey cipher_key(mk.begin(), CIPHER_KEY_LEN);
SymmetricKey mac_key(mk.begin() + CIPHER_KEY_LEN, MAC_KEY_LEN);
InitializationVector iv(mk.begin() + CIPHER_KEY_LEN + MAC_KEY_LEN,
CIPHER_IV_LEN);
Pipe pipe(new Fork(
get_cipher("Serpent/CTR-BE", cipher_key, iv, ENCRYPTION),
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 Integrity_Failure("CryptoBox integrity failure");
return pipe.read_all_as_string(0);
}
}
}
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