olm/src/sas.c

/* Copyright 2018-2019 New Vector 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.
 */

#include "olm/sas.h"
#include "olm/base64.h"
#include "olm/crypto.h"
#include "olm/error.h"
#include "olm/memory.h"

struct OlmSAS {
    enum OlmErrorCode last_error;
    struct _olm_curve25519_key_pair curve25519_key;
    uint8_t secret[CURVE25519_SHARED_SECRET_LENGTH];
    int their_key_set;
};

const char * olm_sas_last_error(
    OlmSAS * sas
) {
    return _olm_error_to_string(sas->last_error);
}

size_t olm_sas_size(void) {
    return sizeof(OlmSAS);
}

OlmSAS * olm_sas(
    void * memory
) {
    _olm_unset(memory, sizeof(OlmSAS));
    return (OlmSAS *) memory;
}

size_t olm_clear_sas(
    OlmSAS * sas
) {
    _olm_unset(sas, sizeof(OlmSAS));
    return sizeof(OlmSAS);
}

size_t olm_create_sas_random_length(OlmSAS * sas) {
    return CURVE25519_KEY_LENGTH;
}

size_t olm_create_sas(
    OlmSAS * sas,
    void * random, size_t random_length
) {
    if (random_length < olm_create_sas_random_length(sas)) {
        sas->last_error = OLM_NOT_ENOUGH_RANDOM;
        return (size_t)-1;
    }
    _olm_crypto_curve25519_generate_key((uint8_t *) random, &sas->curve25519_key);
    sas->their_key_set = 0;
    return 0;
}

size_t olm_sas_pubkey_length(OlmSAS * sas) {
    return _olm_encode_base64_length(CURVE25519_KEY_LENGTH);
}

size_t olm_sas_get_pubkey(
    OlmSAS * sas,
    void * pubkey, size_t pubkey_length
) {
    if (pubkey_length < olm_sas_pubkey_length(sas)) {
        sas->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL;
        return (size_t)-1;
    }
    _olm_encode_base64(
        (const uint8_t *)sas->curve25519_key.public_key.public_key,
        CURVE25519_KEY_LENGTH,
        (uint8_t *)pubkey
    );
    return 0;
}

size_t olm_sas_set_their_key(
    OlmSAS *sas,
    void * their_key, size_t their_key_length
) {
    if (their_key_length < olm_sas_pubkey_length(sas)) {
        sas->last_error = OLM_INPUT_BUFFER_TOO_SMALL;
        return (size_t)-1;
    }
    _olm_decode_base64(their_key, their_key_length, their_key);
    _olm_crypto_curve25519_shared_secret(&sas->curve25519_key, their_key, sas->secret);
    sas->their_key_set = 1;
    return 0;
}

int olm_sas_is_their_key_set(
    OlmSAS *sas
) {
    return sas->their_key_set;
}

size_t olm_sas_generate_bytes(
    OlmSAS * sas,
    const void * info, size_t info_length,
    void * output, size_t output_length
) {
    if (!sas->their_key_set) {
        sas->last_error = OLM_SAS_THEIR_KEY_NOT_SET;
        return (size_t)-1;
    }
    _olm_crypto_hkdf_sha256(
        sas->secret, sizeof(sas->secret),
        NULL, 0,
        (const uint8_t *) info, info_length,
        output, output_length
    );
    return 0;
}

size_t olm_sas_mac_length(
    OlmSAS *sas
) {
    return _olm_encode_base64_length(SHA256_OUTPUT_LENGTH);
}

// A version of the calculate mac function that produces base64 strings that are
// compatible with other base64 implementations.
size_t olm_sas_calculate_mac_fixed_base64(
    OlmSAS * sas,
    const void * input, size_t input_length,
    const void * info, size_t info_length,
    void * mac, size_t mac_length
) {
    if (mac_length < olm_sas_mac_length(sas)) {
        sas->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL;
        return (size_t)-1;
    }
    if (!sas->their_key_set) {
        sas->last_error = OLM_SAS_THEIR_KEY_NOT_SET;
        return (size_t)-1;
    }
    uint8_t key[32];
    _olm_crypto_hkdf_sha256(
        sas->secret, sizeof(sas->secret),
        NULL, 0,
        (const uint8_t *) info, info_length,
        key, 32
    );

    uint8_t temp_mac[32];
    _olm_crypto_hmac_sha256(key, 32, input, input_length, temp_mac);
    _olm_encode_base64((const uint8_t *)temp_mac, SHA256_OUTPUT_LENGTH, (uint8_t *)mac);

    return 0;
}


size_t olm_sas_calculate_mac(
    OlmSAS * sas,
    const void * input, size_t input_length,
    const void * info, size_t info_length,
    void * mac, size_t mac_length
) {
    if (mac_length < olm_sas_mac_length(sas)) {
        sas->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL;
        return (size_t)-1;
    }
    if (!sas->their_key_set) {
        sas->last_error = OLM_SAS_THEIR_KEY_NOT_SET;
        return (size_t)-1;
    }
    uint8_t key[32];
    _olm_crypto_hkdf_sha256(
        sas->secret, sizeof(sas->secret),
        NULL, 0,
        (const uint8_t *) info, info_length,
        key, 32
    );
    _olm_crypto_hmac_sha256(key, 32, input, input_length, mac);
    _olm_encode_base64((const uint8_t *)mac, SHA256_OUTPUT_LENGTH, (uint8_t *)mac);
    return 0;
}

// for compatibility with an old version of Riot
size_t olm_sas_calculate_mac_long_kdf(
    OlmSAS * sas,
    const void * input, size_t input_length,
    const void * info, size_t info_length,
    void * mac, size_t mac_length
) {
    if (mac_length < olm_sas_mac_length(sas)) {
        sas->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL;
        return (size_t)-1;
    }
    if (!sas->their_key_set) {
        sas->last_error = OLM_SAS_THEIR_KEY_NOT_SET;
        return (size_t)-1;
    }
    uint8_t key[256];
    _olm_crypto_hkdf_sha256(
        sas->secret, sizeof(sas->secret),
        NULL, 0,
        (const uint8_t *) info, info_length,
        key, 256
    );
    _olm_crypto_hmac_sha256(key, 256, input, input_length, mac);
    _olm_encode_base64((const uint8_t *)mac, SHA256_OUTPUT_LENGTH, (uint8_t *)mac);
    return 0;
}