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Move AES specific details behind a cipher interface

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This commit is contained in:
Mark Haines 2015-06-11 14:20:35 +01:00
parent 8161b56ff0
commit 816435a860
9 changed files with 404 additions and 184 deletions
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127
include/axolotl/cipher.hh Normal file
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@ -0,0 +1,127 @@
/* Copyright 2015 OpenMarket Ltd
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef AXOLOTL_CIPHER_HH_
#define AXOLOTL_CIPHER_HH_
#include <cstdint>
namespace axolotl {
class Cipher {
public:
virtual ~Cipher();
/**
* Returns the length of the message authentication code that will be
* appended to the output.
*/
virtual std::size_t mac_length() const = 0;
/**
* Returns the length of cipher-text for a given length of plain-text.
*/
virtual std::size_t encrypt_ciphertext_length(
std::size_t plaintext_length
) const = 0;
/*
* Encrypts the plain-text into the output buffer and authenticates the
* contents of the output buffer covering both cipher-text and any other
* associated data in the output buffer.
*
* |---------------------------------------output_length-->|
* output |--ciphertext_length-->| |---mac_length-->|
* ciphertext
*
* Returns std::size_t(-1) if the length of the cipher-text or the output
* buffer is too small. Otherwise returns the length of the output buffer.
*/
virtual std::size_t encrypt(
std::uint8_t const * key, std::size_t key_length,
std::uint8_t const * plaintext, std::size_t plaintext_length,
std::uint8_t * ciphertext, std::size_t ciphertext_length,
std::uint8_t * output, std::size_t output_length
) const = 0;
/**
* Returns the maximum length of plain-text that a given length of
* cipher-text can contain.
*/
virtual std::size_t decrypt_max_plaintext_length(
std::size_t ciphertext_length
) const = 0;
/**
* Authenticates the input and decrypts the cipher-text into the plain-text
* buffer.
*
* |----------------------------------------input_length-->|
* input |--ciphertext_length-->| |---mac_length-->|
* ciphertext
*
* Returns std::size_t(-1) if the length of the plain-text buffer is too
* small or if the authentication check fails. Otherwise returns the length
* of the plain text.
*/
virtual std::size_t decrypt(
std::uint8_t const * key, std::size_t key_length,
std::uint8_t const * input, std::size_t input_length,
std::uint8_t const * ciphertext, std::size_t ciphertext_length,
std::uint8_t * plaintext, std::size_t max_plaintext_length
) const = 0;
};
class CipherAesSha256 : public Cipher {
public:
CipherAesSha256(
std::uint8_t const * kdf_info, std::size_t kdf_info_length
);
virtual std::size_t mac_length() const;
virtual std::size_t encrypt_ciphertext_length(
std::size_t plaintext_length
) const;
virtual std::size_t encrypt(
std::uint8_t const * key, std::size_t key_length,
std::uint8_t const * plaintext, std::size_t plaintext_length,
std::uint8_t * ciphertext, std::size_t ciphertext_length,
std::uint8_t * output, std::size_t output_length
) const;
virtual std::size_t decrypt_max_plaintext_length(
std::size_t ciphertext_length
) const;
virtual std::size_t decrypt(
std::uint8_t const * key, std::size_t key_length,
std::uint8_t const * input, std::size_t input_length,
std::uint8_t const * ciphertext, std::size_t ciphertext_length,
std::uint8_t * plaintext, std::size_t max_plaintext_length
) const;
private:
std::uint8_t const * kdf_info;
std::size_t kdf_info_length;
};
} // namespace
#endif /* AXOLOTL_CIPHER_HH_ */

2
include/axolotl/list.hh
View file

@ -92,7 +92,7 @@ public:
}
List<T, max_size> & operator=(List<T, max_size> const & other) {
if (this = &other) {
if (this == &other) {
return *this;
}
T * this_pos = _data;

22
include/axolotl/message.hh
View file

@ -30,22 +30,17 @@ std::size_t encode_message_length(
struct MessageWriter {
std::size_t body_length;
std::uint8_t * ratchet_key;
std::uint8_t * ciphertext;
std::uint8_t * mac;
};
struct MessageReader {
std::size_t body_length;
std::uint8_t version;
std::uint32_t counter;
std::size_t ratchet_key_length;
std::size_t ciphertext_length;
std::uint8_t const * ratchet_key;
std::uint8_t const * ciphertext;
std::uint8_t const * mac;
std::uint8_t const * input; std::size_t input_length;
std::uint8_t const * ratchet_key; std::size_t ratchet_key_length;
std::uint8_t const * ciphertext; std::size_t ciphertext_length;
};
@ -53,7 +48,9 @@ struct MessageReader {
* Writes the message headers into the output buffer.
* Returns a writer struct populated with pointers into the output buffer.
*/
MessageWriter encode_message(
void encode_message(
MessageWriter & writer,
std::uint8_t version,
std::uint32_t counter,
std::size_t ratchet_key_length,
@ -64,10 +61,11 @@ MessageWriter encode_message(
/**
* Reads the message headers from the input buffer.
* Returns a reader struct populated with pointers into the input buffer.
* On failure the returned body_length will be 0.
* Populates the reader struct with pointers into the input buffer.
* On failure returns std::size_t(-1).
*/
MessageReader decode_message(
std::size_t decode_message(
MessageReader & reader,
std::uint8_t const * input, std::size_t input_length,
std::size_t mac_length
);

32
include/axolotl/ratchet.hh
View file

@ -18,6 +18,8 @@
namespace axolotl {
class Cipher;
typedef std::uint8_t SharedKey[32];
@ -29,9 +31,7 @@ struct ChainKey {
struct MessageKey {
std::uint32_t index;
Aes256Key cipher_key;
SharedKey mac_key;
Aes256Iv iv;
SharedKey key;
};
@ -72,21 +72,23 @@ struct KdfInfo {
std::size_t root_info_length;
std::uint8_t const * ratchet_info;
std::size_t ratchet_info_length;
std::uint8_t const * message_info;
std::size_t message_info_length;
};
struct Session {
Session(
KdfInfo const & kdf_info
KdfInfo const & kdf_info,
Cipher const & ratchet_cipher
);
/** A some strings identifing the application to feed into the KDF. */
const KdfInfo &kdf_info;
/** A some strings identifying the application to feed into the KDF. */
KdfInfo const & kdf_info;
/** The last error that happened encypting or decrypting a message. */
/** The AEAD cipher to use for encrypting messages. */
Cipher const & ratchet_cipher;
/** The last error that happened encrypting or decrypting a message. */
ErrorCode last_error;
/** The root key is used to generate chain keys from the ephemeral keys.
@ -98,7 +100,7 @@ struct Session {
* with a new empheral key when we next send a message. */
List<SenderChain, 1> sender_chain;
/** The receiver chain is used to decrypt recieved messages. We store the
/** The receiver chain is used to decrypt received messages. We store the
* last few chains so we can decrypt any out of order messages we haven't
* received yet. */
List<ReceiverChain, MAX_RECEIVER_CHAINS> receiver_chains;
@ -114,7 +116,7 @@ struct Session {
Curve25519PublicKey const & their_ratchet_key
);
/** Intialise the session using a shared secret and the public/private key
/** Initialise the session using a shared secret and the public/private key
* pair for the first ratchet key */
void initialise_as_alice(
std::uint8_t const * shared_secret, std::size_t shared_secret_length,
@ -150,7 +152,7 @@ struct Session {
* generate a new ephemeral key, or will be 0 bytes otherwise.*/
std::size_t encrypt_random_length();
/** Encrypt some plaintext. Returns the length of the encrypted message
/** Encrypt some plain-text. Returns the length of the encrypted message
* or std::size_t(-1) on failure. On failure last_error will be set with
* an error code. The last_error will be NOT_ENOUGH_RANDOM if the number
* of random bytes is too small. The last_error will be
@ -161,16 +163,16 @@ struct Session {
std::uint8_t * output, std::size_t max_output_length
);
/** An upper bound on the number of bytes of plaintext the decrypt method
/** An upper bound on the number of bytes of plain-text the decrypt method
* will write for a given input message length. */
std::size_t decrypt_max_plaintext_length(
std::size_t input_length
);
/** Decrypt a message. Returns the length of the decrypted plaintext or
/** Decrypt a message. Returns the length of the decrypted plain-text or
* std::size_t(-1) on failure. On failure last_error will be set with an
* error code. The last_error will be OUTPUT_BUFFER_TOO_SMALL if the
* plaintext buffer is too small. The last_error will be
* plain-text buffer is too small. The last_error will be
* BAD_MESSAGE_VERSION if the message was encrypted with an unsupported
* version of the protocol. The last_error will be BAD_MESSAGE_FORMAT if
* the message headers could not be decoded. The last_error will be

125
src/cipher.cpp Normal file
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@ -0,0 +1,125 @@
#include "axolotl/cipher.hh"
#include "axolotl/crypto.hh"
#include "axolotl/memory.hh"
#include <cstring>
axolotl::Cipher::~Cipher() {
}
namespace {
static const std::size_t SHA256_LENGTH = 32;
struct DerivedKeys {
axolotl::Aes256Key aes_key;
std::uint8_t mac_key[SHA256_LENGTH];
axolotl::Aes256Iv aes_iv;
};
static void derive_keys(
std::uint8_t const * kdf_info, std::size_t kdf_info_length,
std::uint8_t const * key, std::size_t key_length,
DerivedKeys & keys
) {
std::uint8_t derived_secrets[80];
axolotl::hkdf_sha256(
key, key_length,
NULL, 0,
kdf_info, kdf_info_length,
derived_secrets, sizeof(derived_secrets)
);
std::memcpy(keys.aes_key.key, derived_secrets, 32);
std::memcpy(keys.mac_key, derived_secrets + 32, 32);
std::memcpy(keys.aes_iv.iv, derived_secrets + 64, 16);
axolotl::unset(derived_secrets);
}
static const std::size_t MAC_LENGTH = 8;
} // namespace
axolotl::CipherAesSha256::CipherAesSha256(
std::uint8_t const * kdf_info, std::size_t kdf_info_length
) : kdf_info(kdf_info), kdf_info_length(kdf_info_length) {
}
std::size_t axolotl::CipherAesSha256::mac_length() const {
return MAC_LENGTH;
}
std::size_t axolotl::CipherAesSha256::encrypt_ciphertext_length(
std::size_t plaintext_length
) const {
return axolotl::aes_encrypt_cbc_length(plaintext_length);
}
std::size_t axolotl::CipherAesSha256::encrypt(
std::uint8_t const * key, std::size_t key_length,
std::uint8_t const * plaintext, std::size_t plaintext_length,
std::uint8_t * ciphertext, std::size_t ciphertext_length,
std::uint8_t * output, std::size_t output_length
) const {
if (encrypt_ciphertext_length(plaintext_length) < ciphertext_length) {
return std::size_t(-1);
}
struct DerivedKeys keys;
std::uint8_t mac[SHA256_LENGTH];
derive_keys(kdf_info, kdf_info_length, key, key_length, keys);
axolotl::aes_encrypt_cbc(
keys.aes_key, keys.aes_iv, plaintext, plaintext_length, ciphertext
);
axolotl::hmac_sha256(
keys.mac_key, SHA256_LENGTH, output, output_length - MAC_LENGTH, mac
);
std::memcpy(output + output_length - MAC_LENGTH, mac, MAC_LENGTH);
axolotl::unset(keys);
return output_length;
}
std::size_t axolotl::CipherAesSha256::decrypt_max_plaintext_length(
std::size_t ciphertext_length
) const {
return ciphertext_length;
}
std::size_t axolotl::CipherAesSha256::decrypt(
std::uint8_t const * key, std::size_t key_length,
std::uint8_t const * input, std::size_t input_length,
std::uint8_t const * ciphertext, std::size_t ciphertext_length,
std::uint8_t * plaintext, std::size_t max_plaintext_length
) const {
DerivedKeys keys;
std::uint8_t mac[SHA256_LENGTH];
derive_keys(kdf_info, kdf_info_length, key, key_length, keys);
axolotl::hmac_sha256(
keys.mac_key, SHA256_LENGTH, input, input_length - MAC_LENGTH, mac
);
std::uint8_t const * input_mac = input + input_length - MAC_LENGTH;
if (!axolotl::is_equal(input_mac, mac, MAC_LENGTH)) {
axolotl::unset(keys);
return std::size_t(-1);
}
std::size_t plaintext_length = axolotl::aes_decrypt_cbc(
keys.aes_key, keys.aes_iv, ciphertext, ciphertext_length, plaintext
);
axolotl::unset(keys);
return plaintext_length;
}

39
src/message.cpp
View file

@ -94,55 +94,52 @@ std::size_t axolotl::encode_message_length(
length += 1 + varstring_length(ratchet_key_length);
length += 1 + varint_length(counter);
length += 1 + varstring_length(ciphertext_length);
return length + mac_length;
length += mac_length;
return length;
}
axolotl::MessageWriter axolotl::encode_message(
void axolotl::encode_message(
axolotl::MessageWriter & writer,
std::uint8_t version,
std::uint32_t counter,
std::size_t ratchet_key_length,
std::size_t ciphertext_length,
std::uint8_t * output
) {
axolotl::MessageWriter result;
std::uint8_t * pos = output;
*(pos++) = version;
*(pos++) = COUNTER_TAG;
pos = varint_encode(pos, counter);
*(pos++) = RATCHET_KEY_TAG;
pos = varint_encode(pos, ratchet_key_length);
result.ratchet_key = pos;
writer.ratchet_key = pos;
pos += ratchet_key_length;
*(pos++) = CIPHERTEXT_TAG;
pos = varint_encode(pos, ciphertext_length);
result.ciphertext = pos;
writer.ciphertext = pos;
pos += ciphertext_length;
result.body_length = pos - output;
result.mac = pos;
return result;
}
axolotl::MessageReader axolotl::decode_message(
std::size_t axolotl::decode_message(
axolotl::MessageReader & reader,
std::uint8_t const * input, std::size_t input_length,
std::size_t mac_length
) {
axolotl::MessageReader result;
result.body_length = 0;
std::uint8_t const * pos = input;
std::uint8_t const * end = input + input_length - mac_length;
std::uint8_t flags = 0;
result.mac = end;
std::size_t result = std::size_t(-1);
if (pos == end) return result;
result.version = *(pos++);
reader.version = *(pos++);
while (pos != end) {
uint8_t tag = *(pos);
if (tag == COUNTER_TAG) {
++pos;
std::uint8_t const * counter_start = pos;
pos = varint_skip(pos, end);
result.counter = varint_decode<std::uint32_t>(counter_start, pos);
reader.counter = varint_decode<std::uint32_t>(counter_start, pos);
flags |= 1;
} else if (tag == RATCHET_KEY_TAG) {
++pos;
@ -150,8 +147,8 @@ axolotl::MessageReader axolotl::decode_message(
pos = varint_skip(pos, end);
std::size_t len = varint_decode<std::size_t>(len_start, pos);
if (len > end - pos) return result;
result.ratchet_key_length = len;
result.ratchet_key = pos;
reader.ratchet_key_length = len;
reader.ratchet_key = pos;
pos += len;
flags |= 2;
} else if (tag == CIPHERTEXT_TAG) {
@ -160,8 +157,8 @@ axolotl::MessageReader axolotl::decode_message(
pos = varint_skip(pos, end);
std::size_t len = varint_decode<std::size_t>(len_start, pos);
if (len > end - pos) return result;
result.ciphertext_length = len;
result.ciphertext = pos;
reader.ciphertext_length = len;
reader.ciphertext = pos;
pos += len;
flags |= 4;
} else if (tag & 0x7 == 0) {
@ -174,11 +171,13 @@ axolotl::MessageReader axolotl::decode_message(
if (len > end - pos) return result;
pos += len;
} else {
return result;
return std::size_t(-1);
}
}
if (flags == 0x7) {
result.body_length = end - input;
reader.input = input;
reader.input_length = input_length;
return std::size_t(pos - input);
}
return result;
}

214
src/ratchet.cpp
View file

@ -15,13 +15,13 @@
#include "axolotl/ratchet.hh"
#include "axolotl/message.hh"
#include "axolotl/memory.hh"
#include "axolotl/cipher.hh"
#include <cstring>
namespace {
std::uint8_t PROTOCOL_VERSION = 3;
std::size_t MAC_LENGTH = 8;
std::size_t KEY_LENGTH = axolotl::Curve25519PublicKey::LENGTH;
std::uint8_t MESSAGE_KEY_SEED[1] = {0x01};
std::uint8_t CHAIN_KEY_SEED[1] = {0x02};
@ -70,59 +70,43 @@ void create_message_keys(
axolotl::KdfInfo const & info,
axolotl::MessageKey & message_key
) {
axolotl::SharedKey secret;
axolotl::hmac_sha256(
chain_key.key, sizeof(chain_key.key),
MESSAGE_KEY_SEED, sizeof(MESSAGE_KEY_SEED),
secret
message_key.key
);
std::uint8_t derived_secrets[80];
axolotl::hkdf_sha256(
secret, sizeof(secret),
NULL, 0,
info.message_info, info.message_info_length,
derived_secrets, sizeof(derived_secrets)
);
std::memcpy(message_key.cipher_key.key, derived_secrets, 32);
std::memcpy(message_key.mac_key, derived_secrets + 32, 32);
std::memcpy(message_key.iv.iv, derived_secrets + 64, 16);
message_key.index = chain_key.index;
axolotl::unset(derived_secrets);
axolotl::unset(secret);
}
bool verify_mac(
std::size_t verify_mac_and_decrypt(
axolotl::Cipher const & cipher,
axolotl::MessageKey const & message_key,
std::uint8_t const * input,
axolotl::MessageReader const & reader
axolotl::MessageReader const & reader,
std::uint8_t * plaintext, std::size_t max_plaintext_length
) {
std::uint8_t mac[axolotl::HMAC_SHA256_OUTPUT_LENGTH];
axolotl::hmac_sha256(
message_key.mac_key, sizeof(message_key.mac_key),
input, reader.body_length,
mac
return cipher.decrypt(
message_key.key, sizeof(message_key.key),
reader.input, reader.input_length,
reader.ciphertext, reader.ciphertext_length,
plaintext, max_plaintext_length
);
bool result = axolotl::is_equal(mac, reader.mac, MAC_LENGTH);
axolotl::unset(mac);
return result;
}
bool verify_mac_for_existing_chain(
std::size_t verify_mac_and_decrypt_for_existing_chain(
axolotl::Session const & session,
axolotl::ChainKey const & chain,
std::uint8_t const * input,
axolotl::MessageReader const & reader
axolotl::MessageReader const & reader,
std::uint8_t * plaintext, std::size_t max_plaintext_length
) {
if (reader.counter < chain.index) {
return false;
return std::size_t(-1);
}
/* Limit the number of hashes we're prepared to compute */
if (reader.counter - chain.index > MAX_MESSAGE_GAP) {
return false;
return std::size_t(-1);
}
axolotl::ChainKey new_chain = chain;
@ -134,16 +118,20 @@ bool verify_mac_for_existing_chain(
axolotl::MessageKey message_key;
create_message_keys(new_chain, session.kdf_info, message_key);
bool result = verify_mac(message_key, input, reader);
std::size_t result = verify_mac_and_decrypt(
session.ratchet_cipher, message_key, reader,
plaintext, max_plaintext_length
);
axolotl::unset(new_chain);
return result;
}
bool verify_mac_for_new_chain(
std::size_t verify_mac_and_decrypt_for_new_chain(
axolotl::Session const & session,
std::uint8_t const * input,
axolotl::MessageReader const & reader
axolotl::MessageReader const & reader,
std::uint8_t * plaintext, std::size_t max_plaintext_length
) {
axolotl::SharedKey new_root_key;
axolotl::ReceiverChain new_chain;
@ -168,8 +156,9 @@ bool verify_mac_for_new_chain(
new_root_key, new_chain.chain_key
);
bool result = verify_mac_for_existing_chain(
session, new_chain.chain_key, input, reader
std::size_t result = verify_mac_and_decrypt_for_existing_chain(
session, new_chain.chain_key, reader,
plaintext, max_plaintext_length
);
axolotl::unset(new_root_key);
axolotl::unset(new_chain);
@ -180,8 +169,11 @@ bool verify_mac_for_new_chain(
axolotl::Session::Session(
axolotl::KdfInfo const & kdf_info
) : kdf_info(kdf_info), last_error(axolotl::ErrorCode::SUCCESS) {
axolotl::KdfInfo const & kdf_info,
Cipher const & ratchet_cipher
) : kdf_info(kdf_info),
ratchet_cipher(ratchet_cipher),
last_error(axolotl::ErrorCode::SUCCESS) {
}
@ -232,7 +224,7 @@ std::size_t axolotl::Session::pickle_max_output_length() {
pickle_length += sender_chain.size() * send_chain_length;
pickle_length += receiver_chains.size() * recv_chain_length;
pickle_length += skipped_message_keys.size() * skip_key_length;
return axolotl::aes_encrypt_cbc_length(pickle_length) + MAC_LENGTH;
return pickle_length;
}
namespace {
@ -299,11 +291,10 @@ std::size_t axolotl::Session::pickle(
}
for (const axolotl::SkippedMessageKey &key : skipped_message_keys) {
pos = pickle_counter(pos, key.message_key.index);
pos = pickle_bytes(pos, 32, key.message_key.cipher_key.key);
pos = pickle_bytes(pos, 32, key.message_key.mac_key);
pos = pickle_bytes(pos, 16, key.message_key.iv.iv);
pos = pickle_bytes(pos, 32, key.message_key.key);
pos = pickle_bytes(pos, 32, key.ratchet_key.public_key);
}
return pos - output;
}
std::size_t axolotl::Session::unpickle(
@ -352,11 +343,10 @@ std::size_t axolotl::Session::unpickle(
skipped_message_keys.end()
);
pos = unpickle_counter(pos, key.message_key.index);
pos = unpickle_bytes(pos, 32, key.message_key.cipher_key.key);
pos = unpickle_bytes(pos, 32, key.message_key.mac_key);
pos = unpickle_bytes(pos, 16, key.message_key.iv.iv);
pos = unpickle_bytes(pos, 32, key.message_key.key);
pos = unpickle_bytes(pos, 32, key.ratchet_key.public_key);
}
return pos - input;
}
@ -369,7 +359,7 @@ std::size_t axolotl::Session::encrypt_max_output_length(
}
std::size_t padded = axolotl::aes_encrypt_cbc_length(plaintext_length);
return axolotl::encode_message_length(
counter, KEY_LENGTH, padded, MAC_LENGTH
counter, KEY_LENGTH, padded, ratchet_cipher.mac_length()
);
}
@ -384,11 +374,13 @@ std::size_t axolotl::Session::encrypt(
std::uint8_t const * random, std::size_t random_length,
std::uint8_t * output, std::size_t max_output_length
) {
std::size_t output_length = encrypt_max_output_length(plaintext_length);
if (random_length < encrypt_random_length()) {
last_error = axolotl::ErrorCode::NOT_ENOUGH_RANDOM;
return std::size_t(-1);
}
if (max_output_length < encrypt_max_output_length(plaintext_length)) {
if (max_output_length < output_length) {
last_error = axolotl::ErrorCode::OUTPUT_BUFFER_TOO_SMALL;
return std::size_t(-1);
}
@ -409,32 +401,29 @@ std::size_t axolotl::Session::encrypt(
create_message_keys(sender_chain[0].chain_key, kdf_info, keys);
advance_chain_key(sender_chain[0].chain_key, sender_chain[0].chain_key);
std::size_t padded = axolotl::aes_encrypt_cbc_length(plaintext_length);
std::size_t ciphertext_length = ratchet_cipher.encrypt_ciphertext_length(
plaintext_length
);
std::uint32_t counter = keys.index;
Curve25519PublicKey const & ratchet_key = sender_chain[0].ratchet_key;
axolotl::MessageWriter writer(axolotl::encode_message(
PROTOCOL_VERSION, counter, KEY_LENGTH, padded, output
));
axolotl::MessageWriter writer;
axolotl::encode_message(
writer, PROTOCOL_VERSION, counter, KEY_LENGTH, ciphertext_length, output
);
std::memcpy(writer.ratchet_key, ratchet_key.public_key, KEY_LENGTH);
axolotl::aes_encrypt_cbc(
keys.cipher_key, keys.iv,
ratchet_cipher.encrypt(
keys.key, sizeof(keys.key),
plaintext, plaintext_length,
writer.ciphertext
writer.ciphertext, ciphertext_length,
output, output_length
);
std::uint8_t mac[axolotl::HMAC_SHA256_OUTPUT_LENGTH];
axolotl::hmac_sha256(
keys.mac_key, sizeof(keys.mac_key),
output, writer.body_length,
mac
);
std::memcpy(writer.mac, mac, MAC_LENGTH);
axolotl::unset(keys);
return writer.body_length + MAC_LENGTH;
return output_length;
}
@ -454,16 +443,17 @@ std::size_t axolotl::Session::decrypt(
return std::size_t(-1);
}
axolotl::MessageReader reader(axolotl::decode_message(
input, input_length, MAC_LENGTH
));
axolotl::MessageReader reader;
std::size_t body_length = axolotl::decode_message(
reader, input, input_length, ratchet_cipher.mac_length()
);
if (reader.version != PROTOCOL_VERSION) {
last_error = axolotl::ErrorCode::BAD_MESSAGE_VERSION;
return std::size_t(-1);
}
if (reader.body_length == 0 || reader.ratchet_key_length != KEY_LENGTH) {
if (body_length == size_t(-1) || reader.ratchet_key_length != KEY_LENGTH) {
last_error = axolotl::ErrorCode::BAD_MESSAGE_FORMAT;
return std::size_t(-1);
}
@ -479,40 +469,30 @@ std::size_t axolotl::Session::decrypt(
}
}
std::size_t result = std::size_t(-1);
if (!chain) {
if (!verify_mac_for_new_chain(*this, input, reader)) {
last_error = axolotl::ErrorCode::BAD_MESSAGE_MAC;
return std::size_t(-1);
}
} else {
if (chain->chain_key.index > reader.counter) {
/* Chain already advanced beyond the key for this message
* Check if the message keys are in the skipped key list. */
for (axolotl::SkippedMessageKey & skipped : skipped_message_keys) {
if (reader.counter == skipped.message_key.index
&& 0 == std::memcmp(
skipped.ratchet_key.public_key, reader.ratchet_key,
KEY_LENGTH
)
) {
/* Found the key for this message. Check the MAC. */
if (!verify_mac(skipped.message_key, input, reader)) {
last_error = axolotl::ErrorCode::BAD_MESSAGE_MAC;
return std::size_t(-1);
}
result = verify_mac_and_decrypt_for_new_chain(
*this, reader, plaintext, max_plaintext_length
);
} else if (chain->chain_key.index > reader.counter) {
/* Chain already advanced beyond the key for this message
* Check if the message keys are in the skipped key list. */
for (axolotl::SkippedMessageKey & skipped : skipped_message_keys) {
if (reader.counter == skipped.message_key.index
&& 0 == std::memcmp(
skipped.ratchet_key.public_key, reader.ratchet_key,
KEY_LENGTH
)
) {
/* Found the key for this message. Check the MAC. */
std::size_t result = axolotl::aes_decrypt_cbc(
skipped.message_key.cipher_key,
skipped.message_key.iv,
reader.ciphertext, reader.ciphertext_length,
plaintext
);
if (result == std::size_t(-1)) {
last_error = axolotl::ErrorCode::BAD_MESSAGE_MAC;
return result;
}
result = verify_mac_and_decrypt(
ratchet_cipher, skipped.message_key, reader,
plaintext, max_plaintext_length
);
if (result != std::size_t(-1)) {
/* Remove the key from the skipped keys now that we've
* decoded the message it corresponds to. */
axolotl::unset(skipped);
@ -520,15 +500,16 @@ std::size_t axolotl::Session::decrypt(
return result;
}
}
/* No matching keys for the message, fail with bad mac */
last_error = axolotl::ErrorCode::BAD_MESSAGE_MAC;
return std::size_t(-1);
} else if (!verify_mac_for_existing_chain(
*this, chain->chain_key, input, reader
)) {
last_error = axolotl::ErrorCode::BAD_MESSAGE_MAC;
return std::size_t(-1);
}
} else {
result = verify_mac_and_decrypt_for_existing_chain(
*this, chain->chain_key, reader, plaintext, max_plaintext_length
);
}
if (result == std::size_t(-1)) {
last_error = axolotl::ErrorCode::BAD_MESSAGE_MAC;
return std::size_t(-1);
}
if (!chain) {
@ -555,22 +536,7 @@ std::size_t axolotl::Session::decrypt(
advance_chain_key(chain->chain_key, chain->chain_key);
}
axolotl::MessageKey message_key;
create_message_keys(chain->chain_key, kdf_info, message_key);
std::size_t result = axolotl::aes_decrypt_cbc(
message_key.cipher_key,
message_key.iv,
reader.ciphertext, reader.ciphertext_length,
plaintext
);
axolotl::unset(message_key);
advance_chain_key(chain->chain_key, chain->chain_key);
if (result == std::size_t(-1)) {
last_error = axolotl::ErrorCode::BAD_MESSAGE_MAC;
return std::size_t(-1);
} else {
return result;
}
return result;
}

11
tests/test_message.cpp
View file

@ -27,9 +27,9 @@ std::uint8_t hmacsha2[9] = "hmacsha2";
TestCase test_case("Message decode test");
axolotl::MessageReader reader(axolotl::decode_message(message1, 35, 8));
axolotl::MessageReader reader;
axolotl::decode_message(reader, message1, 35, 8);
assert_equals(std::size_t(27), reader.body_length);
assert_equals(std::uint8_t(3), reader.version);
assert_equals(std::uint32_t(1), reader.counter);
assert_equals(std::size_t(10), reader.ratchet_key_length);
@ -37,7 +37,6 @@ assert_equals(std::size_t(10), reader.ciphertext_length);
assert_equals(ratchetkey, reader.ratchet_key, 10);
assert_equals(ciphertext, reader.ciphertext, 10);
assert_equals(hmacsha2, reader.mac, 8);
} /* Message decode test */
@ -51,12 +50,12 @@ assert_equals(std::size_t(35), length);
std::uint8_t output[length];
axolotl::MessageWriter writer(axolotl::encode_message(3, 1, 10, 10, output));
assert_equals(std::size_t(27), writer.body_length);
axolotl::MessageWriter writer;
axolotl::encode_message(writer, 3, 1, 10, 10, output);
std::memcpy(writer.ratchet_key, ratchetkey, 10);
std::memcpy(writer.ciphertext, ciphertext, 10);
std::memcpy(writer.mac, hmacsha2, 8);
std::memcpy(output + length - 8, hmacsha2, 8);
assert_equals(message2, output, 35);

16
tests/test_ratchet.cpp
View file

@ -13,6 +13,7 @@
* limitations under the License.
*/
#include "axolotl/ratchet.hh"
#include "axolotl/cipher.hh"
#include "unittest.hh"
@ -24,10 +25,13 @@ std::uint8_t message_info[] = "AxolotlMessageKeys";
axolotl::KdfInfo kdf_info = {
root_info, sizeof(root_info) - 1,
ratchet_info, sizeof(ratchet_info - 1),
message_info, sizeof(ratchet_info - 1)
ratchet_info, sizeof(ratchet_info) - 1
};
axolotl::CipherAesSha256 cipher(
message_info, sizeof(message_info) - 1
);
std::uint8_t random_bytes[] = "0123456789ABDEF0123456789ABCDEF";
axolotl::Curve25519KeyPair bob_key;
axolotl::generate_key(random_bytes, bob_key);
@ -37,8 +41,8 @@ std::uint8_t shared_secret[] = "A secret";
{ /* Send/Receive test case */
TestCase test_case("Axolotl Send/Receive");
axolotl::Session alice(kdf_info);
axolotl::Session bob(kdf_info);
axolotl::Session alice(kdf_info, cipher);
axolotl::Session bob(kdf_info, cipher);
alice.initialise_as_bob(shared_secret, sizeof(shared_secret) - 1, bob_key);
bob.initialise_as_alice(shared_secret, sizeof(shared_secret) - 1, bob_key);
@ -106,8 +110,8 @@ std::size_t encrypt_length, decrypt_length;
TestCase test_case("Axolotl Out of Order");
axolotl::Session alice(kdf_info);
axolotl::Session bob(kdf_info);
axolotl::Session alice(kdf_info, cipher);
axolotl::Session bob(kdf_info, cipher);
alice.initialise_as_bob(shared_secret, sizeof(shared_secret) - 1, bob_key);
bob.initialise_as_alice(shared_secret, sizeof(shared_secret) - 1, bob_key);