initial commit: start implementing the crypto primitives

1 files changed, 223 insertions, 0 deletions

diff --git a/src/crypto.cpp b/src/crypto.cpp
new file mode 100644
index 0000000..c1ef88a
--- /dev/null
+++ b/src/crypto.cpp
@@ -0,0 +1,223 @@
+#include "axolotl/crypto.hh"
+#include <cstring>
+
+extern "C" {
+
+int curve25519_donna(
+    uint8_t * output,
+    const uint8_t * secret,
+    const uint8_t * basepoint
+);
+
+#include "crypto-algorithms/aes.h"
+#include "crypto-algorithms/sha256.h"
+
+}
+
+
+namespace {
+
+static const std::uint8_t CURVE25519_BASEPOINT[32] = {9};
+static const std::size_t AES_BLOCK_LENGTH = 16;
+static const std::size_t SHA256_BLOCK_LENGTH = 32;
+static const std::uint8_t HKDF_DEFAULT_SALT[32] = {};
+
+template<std::size_t block_size>
+inline static void xor_block(
+    std::uint8_t * block,
+    std::uint8_t const * input
+) {
+    for (std::size_t i = 0; i < block_size; ++i) {
+        block[i] ^= input[i];
+    }
+}
+
+
+inline static void hmac_sha256_key(
+    std::uint8_t const * input_key, std::size_t input_key_length,
+    std::uint8_t * hmac_key
+) {
+    if (input_key_length > SHA256_BLOCK_LENGTH) {
+        ::SHA256_CTX context;
+        ::sha256_init(&context);
+        ::sha256_update(&context, input_key, input_key_length);
+        ::sha256_final(&context, hmac_key);
+    } else {
+        std::memset(hmac_key, 0, SHA256_BLOCK_LENGTH);
+        std::memcpy(hmac_key, input_key, input_key_length);
+    }
+}
+
+
+inline void hmac_sha256_init(
+    ::SHA256_CTX * context,
+    std::uint8_t const * hmac_key
+) {
+    std::uint8_t i_pad[SHA256_BLOCK_LENGTH];
+    std::memcpy(i_pad, hmac_key, SHA256_BLOCK_LENGTH);
+    for (std::size_t i = 0; i < SHA256_BLOCK_LENGTH; ++i) {
+        i_pad[i] ^= 0x5C;
+    }
+    ::sha256_init(context);
+    ::sha256_update(context, i_pad, SHA256_BLOCK_LENGTH);
+    std::memset(i_pad, 0, sizeof(i_pad));
+}
+
+
+inline void hmac_sha256_final(
+    ::SHA256_CTX * context,
+    std::uint8_t const * hmac_key,
+    std::uint8_t * output
+) {
+    std::uint8_t o_pad[SHA256_BLOCK_LENGTH];
+    std::memcpy(o_pad, hmac_key, SHA256_BLOCK_LENGTH);
+    for (std::size_t i = 0; i < SHA256_BLOCK_LENGTH; ++i) {
+        o_pad[i] ^= 0x36;
+    }
+    ::SHA256_CTX final_context;
+    ::sha256_init(&final_context);
+    ::sha256_update(&final_context, o_pad, SHA256_BLOCK_LENGTH);
+    ::sha256_final(context, o_pad);
+    ::sha256_update(&final_context, o_pad, SHA256_BLOCK_LENGTH);
+    ::sha256_final(&final_context, output);
+    std::memset(o_pad, 0, sizeof(o_pad));
+}
+
+} // namespace
+
+
+axolotl::Curve25519KeyPair axolotl::generate_key(
+    std::uint8_t const * random_32_bytes
+) {
+    axolotl::Curve25519KeyPair key_pair;
+    std::memcpy(key_pair.private_key, random_32_bytes, 32);
+    ::curve25519_donna(
+        key_pair.public_key, key_pair.private_key, CURVE25519_BASEPOINT
+    );
+    return key_pair;
+}
+
+
+void axolotl::curve25519_shared_secret(
+    axolotl::Curve25519KeyPair const & our_key,
+    axolotl::Curve25519PublicKey const & their_key,
+    std::uint8_t * output
+) {
+    ::curve25519_donna(output, our_key.private_key, their_key.public_key);
+}
+
+
+std::size_t axolotl::aes_pkcs_7_padded_length(
+    std::size_t input_length
+) {
+    return input_length + AES_BLOCK_LENGTH - input_length % AES_BLOCK_LENGTH;
+}
+
+
+void axolotl::aes_pkcs_7_padding(
+    std::uint8_t const * input, std::size_t input_length,
+    std::uint8_t * output
+) {
+    std::memcpy(output, input, input_length);
+    std::size_t padded_length = axolotl::aes_pkcs_7_padded_length(input_length);
+    std::uint8_t padding = padded_length - input_length;
+    for (std::size_t i = input_length; i < padded_length; ++i) {
+        output[i] = padding;
+    }
+}
+
+
+void axolotl::aes_encrypt_cbc(
+    axolotl::Aes256Key const & key,
+    axolotl::Aes256Iv const & iv,
+    std::uint8_t const * input, std::size_t input_length,
+    std::uint8_t * output
+) {
+    std::uint32_t key_schedule[60];
+    ::aes_key_setup(key.key, key_schedule, 256);
+    std::uint8_t input_block[AES_BLOCK_LENGTH];
+    std::memcpy(input_block, iv.iv, AES_BLOCK_LENGTH);
+    for (std::size_t i = 0; i < input_length; i += AES_BLOCK_LENGTH) {
+        xor_block<AES_BLOCK_LENGTH>(input_block, &input[i]);
+        ::aes_encrypt(input_block, &output[i], key_schedule, 256);
+        std::memcpy(input_block, &output[i], AES_BLOCK_LENGTH);
+    }
+    std::memset(key_schedule, 0, sizeof(key_schedule));
+    std::memset(input_block, 0, sizeof(AES_BLOCK_LENGTH));
+}
+
+
+void axolotl::aes_decrypt_cbc(
+    axolotl::Aes256Key const & key,
+    axolotl::Aes256Iv const & iv,
+    std::uint8_t const * input, std::size_t input_length,
+    std::uint8_t * output
+) {
+    std::uint32_t key_schedule[60];
+    ::aes_key_setup(key.key, key_schedule, 256);
+    for (std::size_t i = 0; i < input_length; i += AES_BLOCK_LENGTH) {
+        ::aes_decrypt(&input[i], &output[i], key_schedule, 256);
+        if (i == 0) {
+            xor_block<AES_BLOCK_LENGTH>(&output[i], iv.iv);
+        } else {
+            xor_block<AES_BLOCK_LENGTH>(&output[i], &input[i - AES_BLOCK_LENGTH]);
+        }
+    }
+    std::memset(key_schedule, 0, sizeof(key_schedule));
+}
+
+
+void axolotl::hmac_sha256(
+    std::uint8_t const * key, std::size_t key_length,
+    std::uint8_t const * input, std::size_t input_length,
+    std::uint8_t * output
+) {
+    std::uint8_t hmac_key[SHA256_BLOCK_LENGTH];
+    ::SHA256_CTX context;
+    hmac_sha256_key(key, key_length, hmac_key);
+    hmac_sha256_init(&context, hmac_key);
+    ::sha256_update(&context, input, input_length);
+    hmac_sha256_final(&context, hmac_key, output);
+    std::memset(hmac_key, 0, sizeof(hmac_key));
+}
+
+
+void axolotl::hkdf_sha256(
+    std::uint8_t const * input, std::size_t input_length,
+    std::uint8_t const * info, std::size_t info_length,
+    std::uint8_t const * salt, std::size_t salt_length,
+    std::uint8_t * output, std::size_t output_length
+) {
+    ::SHA256_CTX context;
+    std::uint8_t extract_key[SHA256_BLOCK_LENGTH];
+    std::uint8_t expand_key[SHA256_BLOCK_LENGTH];
+    std::uint8_t step_result[SHA256_BLOCK_LENGTH];
+    std::size_t bytes_remaining = output_length;
+    std::uint8_t iteration = 1;
+    if (!salt) {
+        salt = HKDF_DEFAULT_SALT;
+        salt_length = sizeof(HKDF_DEFAULT_SALT);
+    }
+    /* Expand */
+    hmac_sha256_key(salt, salt_length, extract_key);
+    hmac_sha256_init(&context, extract_key);
+    ::sha256_update(&context, input, input_length);
+    hmac_sha256_final(&context, extract_key, expand_key);
+    /* Extract */
+    hmac_sha256_init(&context, expand_key);
+    ::sha256_update(&context, info, info_length);
+    ::sha256_update(&context, &iteration, 1);
+    hmac_sha256_final(&context, expand_key, step_result);
+    while (bytes_remaining > SHA256_BLOCK_LENGTH) {
+        std::memcpy(output, step_result, SHA256_BLOCK_LENGTH);
+        output += SHA256_BLOCK_LENGTH;
+        bytes_remaining -= SHA256_BLOCK_LENGTH;
+        iteration ++;
+        hmac_sha256_init(&context, expand_key);
+        ::sha256_update(&context, step_result, SHA256_BLOCK_LENGTH);
+        ::sha256_update(&context, info, info_length);
+        ::sha256_update(&context, &iteration, 1);
+        hmac_sha256_final(&context, expand_key, step_result);
+    }
+    std::memcpy(output, step_result, bytes_remaining);
+}