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/*
* Cryptobox Message Routines
* (C) 2009 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/cryptobox.h>
#include <botan/filters.h>
#include <botan/pipe.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 uint32_t CRYPTOBOX_VERSION_CODE = 0xEFC22400;
const size_t VERSION_CODE_LEN = 4;
const size_t CIPHER_KEY_LEN = 32;
const size_t CIPHER_IV_LEN = 16;
const size_t MAC_KEY_LEN = 32;
const size_t MAC_OUTPUT_LEN = 20;
const size_t PBKDF_SALT_LEN = 10;
const size_t PBKDF_ITERATIONS = 8 * 1024;
const size_t PBKDF_OUTPUT_LEN = CIPHER_KEY_LEN + MAC_KEY_LEN + CIPHER_IV_LEN;
const size_t HEADER_LEN = VERSION_CODE_LEN + PBKDF_SALT_LEN + MAC_OUTPUT_LEN;
}
std::string encrypt(const uint8_t input[], size_t input_len,
const std::string& passphrase,
RandomNumberGenerator& rng)
{
/*
Output format is:
version # (4 bytes)
salt (10 bytes)
mac (20 bytes)
ciphertext
*/
secure_vector<uint8_t> out_buf(HEADER_LEN + input_len);
for(size_t i = 0; i != VERSION_CODE_LEN; ++i)
out_buf[i] = get_byte(i, CRYPTOBOX_VERSION_CODE);
rng.randomize(&out_buf[VERSION_CODE_LEN], PBKDF_SALT_LEN);
// space left for MAC here
copy_mem(&out_buf[HEADER_LEN], input, input_len);
// Generate the keys and IV
std::unique_ptr<PBKDF> pbkdf(PBKDF::create_or_throw("PBKDF2(HMAC(SHA-512))"));
OctetString master_key = pbkdf->derive_key(
CIPHER_KEY_LEN + MAC_KEY_LEN + CIPHER_IV_LEN,
passphrase,
&out_buf[VERSION_CODE_LEN],
PBKDF_SALT_LEN,
PBKDF_ITERATIONS);
const uint8_t* mk = master_key.begin();
const uint8_t* cipher_key = mk;
const uint8_t* mac_key = mk + CIPHER_KEY_LEN;
const uint8_t* iv = mk + CIPHER_KEY_LEN + MAC_KEY_LEN;
// Now encrypt and authenticate
std::unique_ptr<Cipher_Mode> ctr(get_cipher_mode("Serpent/CTR-BE", ENCRYPTION));
ctr->set_key(cipher_key, CIPHER_KEY_LEN);
ctr->start(iv, CIPHER_IV_LEN);
ctr->finish(out_buf, HEADER_LEN);
std::unique_ptr<MessageAuthenticationCode> hmac =
MessageAuthenticationCode::create_or_throw("HMAC(SHA-512)");
hmac->set_key(mac_key, MAC_KEY_LEN);
hmac->update(&out_buf[HEADER_LEN], input_len);
// Can't write directly because of MAC truncation
secure_vector<uint8_t> mac = hmac->final();
copy_mem(&out_buf[VERSION_CODE_LEN + PBKDF_SALT_LEN], mac.data(), MAC_OUTPUT_LEN);
return PEM_Code::encode(out_buf, "BOTAN CRYPTOBOX MESSAGE");
}
std::string decrypt(const uint8_t input[], size_t input_len,
const std::string& passphrase)
{
DataSource_Memory input_src(input, input_len);
secure_vector<uint8_t> 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(size_t i = 0; i != VERSION_CODE_LEN; ++i)
if(ciphertext[i] != get_byte(i, CRYPTOBOX_VERSION_CODE))
throw Decoding_Error("Bad CryptoBox version");
const uint8_t* 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 uint8_t* mk = master_key.begin();
SymmetricKey cipher_key(mk, 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 size_t ciphertext_offset =
VERSION_CODE_LEN + PBKDF_SALT_LEN + MAC_OUTPUT_LEN;
pipe.process_msg(&ciphertext[ciphertext_offset],
ciphertext.size() - ciphertext_offset);
uint8_t computed_mac[MAC_OUTPUT_LEN];
BOTAN_ASSERT_EQUAL(MAC_OUTPUT_LEN, pipe.read(computed_mac, MAC_OUTPUT_LEN, 1), "MAC size");
if(!constant_time_compare(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 uint8_t*>(input.data()),
input.size(),
passphrase);
}
}
}
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