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-rw-r--r--src/cipher.cpp125
1 files changed, 125 insertions, 0 deletions
diff --git a/src/cipher.cpp b/src/cipher.cpp
new file mode 100644
index 0000000..86cde88
--- /dev/null
+++ b/src/cipher.cpp
@@ -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;
+}