Replace hard coded references to the 32-byte key length with a constant, add utilities for copying data to and from fixed sized arrays

12 files changed, 219 insertions, 188 deletions

diff --git a/include/olm/crypto.hh b/include/olm/crypto.hh
index b845bfe..7a05f8d 100644
--- a/include/olm/crypto.hh
+++ b/include/olm/crypto.hh
@@ -20,28 +20,27 @@
 
 namespace olm {
 
+static const std::size_t KEY_LENGTH = 32;
+static const std::size_t SIGNATURE_LENGTH = 64;
+static const std::size_t IV_LENGTH = 16;
 
 struct Curve25519PublicKey {
-    static const int LENGTH = 32;
-    std::uint8_t public_key[32];
+    std::uint8_t public_key[KEY_LENGTH];
 };
 
 
 struct Curve25519KeyPair : public Curve25519PublicKey {
-    static const int LENGTH = 64;
-    std::uint8_t private_key[32];
+    std::uint8_t private_key[KEY_LENGTH];
 };
 
 
 struct Ed25519PublicKey {
-    static const int LENGTH = 32;
-    std::uint8_t public_key[32];
+    std::uint8_t public_key[KEY_LENGTH];
 };
 
 
 struct Ed25519KeyPair : public Ed25519PublicKey {
-    static const int LENGTH = 64;
-    std::uint8_t private_key[32];
+    std::uint8_t private_key[KEY_LENGTH];
 };
 
 
@@ -52,9 +51,6 @@ void curve25519_generate_key(
 );
 
 
-const std::size_t CURVE25519_SHARED_SECRET_LENGTH = 32;
-
-
 /** Create a shared secret using our private key and their public key.
  * The output buffer must be at least 32 bytes long. */
 void curve25519_shared_secret(
@@ -109,14 +105,12 @@ bool ed25519_verify(
 
 
 struct Aes256Key {
-    static const int LENGTH = 32;
-    std::uint8_t key[32];
+    std::uint8_t key[KEY_LENGTH];
 };
 
 
 struct Aes256Iv {
-    static const int LENGTH = 16;
-    std::uint8_t iv[16];
+    std::uint8_t iv[IV_LENGTH];
 };
 
 
@@ -156,7 +150,7 @@ void sha256(
 );
 
 
-const std::size_t HMAC_SHA256_OUTPUT_LENGTH = 32;
+const std::size_t SHA256_OUTPUT_LENGTH = 32;
 
 
 /** HMAC: Keyed-Hashing for Message Authentication
diff --git a/include/olm/memory.hh b/include/olm/memory.hh
index b19c74b..128990a 100644
--- a/include/olm/memory.hh
+++ b/include/olm/memory.hh
@@ -14,6 +14,8 @@
  */
 #include <cstddef>
 #include <cstdint>
+#include <cstring>
+#include <type_traits>
 
 namespace olm {
 
@@ -35,4 +37,51 @@ bool is_equal(
     std::size_t length
 );
 
+/** Check if two fixed size arrays are equals */
+template<typename T>
+bool array_equal(
+    T const & array_a,
+    T const & array_b
+) {
+    static_assert(
+        std::is_array<T>::value
+            && std::is_convertible<T, std::uint8_t *>::value
+            && sizeof(T) > 0,
+        "Arguments to array_equal must be std::uint8_t arrays[]."
+    );
+    return is_equal(array_a, array_b, sizeof(T));
+}
+
+/** Copy into a fixed size array */
+template<typename T>
+std::uint8_t const * load_array(
+    T & destination,
+    std::uint8_t const * source
+) {
+    static_assert(
+        std::is_array<T>::value
+            && std::is_convertible<T, std::uint8_t *>::value
+            && sizeof(T) > 0,
+        "The first argument to load_array must be a std::uint8_t array[]."
+    );
+    std::memcpy(destination, source, sizeof(T));
+    return source + sizeof(T);
+}
+
+/** Copy from a fixed size array */
+template<typename T>
+std::uint8_t * store_array(
+    std::uint8_t * destination,
+    T const & source
+) {
+    static_assert(
+        std::is_array<T>::value
+            && std::is_convertible<T, std::uint8_t *>::value
+            && sizeof(T) > 0,
+        "The second argument to store_array must be a std::uint8_t array[]."
+    );
+    std::memcpy(destination, source, sizeof(T));
+    return destination + sizeof(T);
+}
+
 } // namespace olm
diff --git a/include/olm/ratchet.hh b/include/olm/ratchet.hh
index 7274255..2393e5b 100644
--- a/include/olm/ratchet.hh
+++ b/include/olm/ratchet.hh
@@ -21,7 +21,7 @@ namespace olm {
 
 class Cipher;
 
-typedef std::uint8_t SharedKey[32];
+typedef std::uint8_t SharedKey[olm::KEY_LENGTH];
 
 
 struct ChainKey {
diff --git a/src/account.cpp b/src/account.cpp
index d0ef838..43033c8 100644
--- a/src/account.cpp
+++ b/src/account.cpp
@@ -15,6 +15,7 @@
 #include "olm/account.hh"
 #include "olm/base64.hh"
 #include "olm/pickle.hh"
+#include "olm/memory.hh"
 
 olm::Account::Account(
 ) : next_one_time_key_id(0),
@@ -26,7 +27,7 @@ olm::OneTimeKey const * olm::Account::lookup_key(
     olm::Curve25519PublicKey const & public_key
 ) {
     for (olm::OneTimeKey const & key : one_time_keys) {
-        if (0 == memcmp(key.key.public_key, public_key.public_key, 32)) {
+        if (olm::array_equal(key.key.public_key, public_key.public_key)) {
             return &key;
         }
     }
@@ -38,7 +39,7 @@ std::size_t olm::Account::remove_key(
 ) {
     OneTimeKey * i;
     for (i = one_time_keys.begin(); i != one_time_keys.end(); ++i) {
-        if (0 == memcmp(i->key.public_key, public_key.public_key, 32)) {
+        if (olm::array_equal(i->key.public_key, public_key.public_key)) {
             std::uint32_t id = i->id;
             one_time_keys.erase(i);
             return id;
@@ -48,7 +49,7 @@ std::size_t olm::Account::remove_key(
 }
 
 std::size_t olm::Account::new_account_random_length() {
-    return 2 * 32;
+    return 2 * olm::KEY_LENGTH;
 }
 
 std::size_t olm::Account::new_account(
@@ -60,9 +61,8 @@ std::size_t olm::Account::new_account(
     }
 
     olm::ed25519_generate_key(random, identity_keys.ed25519_key);
-    random += 32;
+    random += KEY_LENGTH;
     olm::curve25519_generate_key(random, identity_keys.curve25519_key);
-    random += 32;
 
     return 0;
 }
@@ -107,7 +107,6 @@ std::size_t olm::Account::get_identity_json(
     std::uint8_t * identity_json, std::size_t identity_json_length
 ) {
     std::uint8_t * pos = identity_json;
-    std::uint8_t signature[64];
     size_t expected_length = get_identity_json_length();
 
     if (identity_json_length < expected_length) {
@@ -138,7 +137,7 @@ std::size_t olm::Account::get_identity_json(
 
 std::size_t olm::Account::signature_length(
 ) {
-    return 64;
+    return olm::SIGNATURE_LENGTH;
 }
 
 
@@ -239,7 +238,7 @@ std::size_t olm::Account::max_number_of_one_time_keys(
 std::size_t olm::Account::generate_one_time_keys_random_length(
     std::size_t number_of_keys
 ) {
-    return 32 * number_of_keys;
+    return olm::KEY_LENGTH * number_of_keys;
 }
 
 std::size_t olm::Account::generate_one_time_keys(
@@ -255,7 +254,7 @@ std::size_t olm::Account::generate_one_time_keys(
         key.id = ++next_one_time_key_id;
         key.published = false;
         olm::curve25519_generate_key(random, key.key);
-        random += 32;
+        random += olm::KEY_LENGTH;
     }
     return number_of_keys;
 }
diff --git a/src/cipher.cpp b/src/cipher.cpp
index 2202746..7bb11b8 100644
--- a/src/cipher.cpp
+++ b/src/cipher.cpp
@@ -23,11 +23,9 @@ olm::Cipher::~Cipher() {
 
 namespace {
 
-static const std::size_t SHA256_LENGTH = 32;
-
 struct DerivedKeys {
     olm::Aes256Key aes_key;
-    std::uint8_t mac_key[SHA256_LENGTH];
+    std::uint8_t mac_key[olm::KEY_LENGTH];
     olm::Aes256Iv aes_iv;
 };
 
@@ -37,16 +35,17 @@ static void derive_keys(
     std::uint8_t const * key, std::size_t key_length,
     DerivedKeys & keys
 ) {
-    std::uint8_t derived_secrets[80];
+    std::uint8_t derived_secrets[2 * olm::KEY_LENGTH + olm::IV_LENGTH];
     olm::hkdf_sha256(
         key, key_length,
         nullptr, 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);
+    std::uint8_t const * pos = derived_secrets;
+    pos = olm::load_array(keys.aes_key.key, pos);
+    pos = olm::load_array(keys.mac_key, pos);
+    pos = olm::load_array(keys.aes_iv.iv, pos);
     olm::unset(derived_secrets);
 }
 
@@ -84,7 +83,7 @@ std::size_t olm::CipherAesSha256::encrypt(
         return std::size_t(-1);
     }
     struct DerivedKeys keys;
-    std::uint8_t mac[SHA256_LENGTH];
+    std::uint8_t mac[olm::SHA256_OUTPUT_LENGTH];
 
     derive_keys(kdf_info, kdf_info_length, key, key_length, keys);
 
@@ -93,7 +92,7 @@ std::size_t olm::CipherAesSha256::encrypt(
     );
 
     olm::hmac_sha256(
-        keys.mac_key, SHA256_LENGTH, output, output_length - MAC_LENGTH, mac
+        keys.mac_key, olm::KEY_LENGTH, output, output_length - MAC_LENGTH, mac
     );
 
     std::memcpy(output + output_length - MAC_LENGTH, mac, MAC_LENGTH);
@@ -116,12 +115,12 @@ std::size_t olm::CipherAesSha256::decrypt(
      std::uint8_t * plaintext, std::size_t max_plaintext_length
 ) const {
     DerivedKeys keys;
-    std::uint8_t mac[SHA256_LENGTH];
+    std::uint8_t mac[olm::SHA256_OUTPUT_LENGTH];
 
     derive_keys(kdf_info, kdf_info_length, key, key_length, keys);
 
     olm::hmac_sha256(
-        keys.mac_key, SHA256_LENGTH, input, input_length - MAC_LENGTH, mac
+        keys.mac_key, olm::KEY_LENGTH, input, input_length - MAC_LENGTH, mac
     );
 
     std::uint8_t const * input_mac = input + input_length - MAC_LENGTH;
diff --git a/src/crypto.cpp b/src/crypto.cpp
index fffda4c..8024355 100644
--- a/src/crypto.cpp
+++ b/src/crypto.cpp
@@ -66,8 +66,9 @@ void ed25519_keypair(
 namespace {
 
 static const std::uint8_t CURVE25519_BASEPOINT[32] = {9};
+static const std::size_t AES_KEY_SCHEDULE_LENGTH = 60;
+static const std::size_t AES_KEY_BITS = 8 * olm::KEY_LENGTH;
 static const std::size_t AES_BLOCK_LENGTH = 16;
-static const std::size_t SHA256_HASH_LENGTH = 32;
 static const std::size_t SHA256_BLOCK_LENGTH = 64;
 static const std::uint8_t HKDF_DEFAULT_SALT[32] = {};
 
@@ -119,7 +120,7 @@ inline static void hmac_sha256_final(
     std::uint8_t const * hmac_key,
     std::uint8_t * output
 ) {
-    std::uint8_t o_pad[SHA256_BLOCK_LENGTH + SHA256_HASH_LENGTH];
+    std::uint8_t o_pad[SHA256_BLOCK_LENGTH + olm::SHA256_OUTPUT_LENGTH];
     std::memcpy(o_pad, hmac_key, SHA256_BLOCK_LENGTH);
     for (std::size_t i = 0; i < SHA256_BLOCK_LENGTH; ++i) {
         o_pad[i] ^= 0x5C;
@@ -140,7 +141,7 @@ void olm::curve25519_generate_key(
     std::uint8_t const * random_32_bytes,
     olm::Curve25519KeyPair & key_pair
 ) {
-    std::memcpy(key_pair.private_key, random_32_bytes, 32);
+    std::memcpy(key_pair.private_key, random_32_bytes, KEY_LENGTH);
     ::curve25519_donna(
         key_pair.public_key, key_pair.private_key, CURVE25519_BASEPOINT
     );
@@ -161,9 +162,9 @@ void olm::curve25519_sign(
     std::uint8_t const * message, std::size_t message_length,
     std::uint8_t * output
 ) {
-    std::uint8_t private_key[32];
-    std::uint8_t public_key[32];
-    std::memcpy(private_key, our_key.private_key, 32);
+    std::uint8_t private_key[KEY_LENGTH];
+    std::uint8_t public_key[KEY_LENGTH];
+    std::memcpy(private_key, our_key.private_key, KEY_LENGTH);
     ::ed25519_keypair(private_key, public_key);
     ::ed25519_sign(
         output,
@@ -179,10 +180,10 @@ bool olm::curve25519_verify(
     std::uint8_t const * message, std::size_t message_length,
     std::uint8_t const * signature
 ) {
-    std::uint8_t public_key[32];
-    std::uint8_t signature_buffer[64];
-    std::memcpy(public_key, their_key.public_key, 32);
-    std::memcpy(signature_buffer, signature, 64);
+    std::uint8_t public_key[KEY_LENGTH];
+    std::uint8_t signature_buffer[SIGNATURE_LENGTH];
+    std::memcpy(public_key, their_key.public_key, KEY_LENGTH);
+    std::memcpy(signature_buffer, signature, SIGNATURE_LENGTH);
     ::convert_curve25519_to_ed25519(public_key, signature_buffer);
     return 0 != ::ed25519_verify(
         signature,
@@ -196,7 +197,7 @@ void olm::ed25519_generate_key(
     std::uint8_t const * random_32_bytes,
     olm::Ed25519KeyPair & key_pair
 ) {
-    std::memcpy(key_pair.private_key, random_32_bytes, 32);
+    std::memcpy(key_pair.private_key, random_32_bytes, KEY_LENGTH);
     ::ed25519_keypair(key_pair.private_key, key_pair.public_key);
 }
 
@@ -240,13 +241,13 @@ void olm::aes_encrypt_cbc(
     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::uint32_t key_schedule[AES_KEY_SCHEDULE_LENGTH];
+    ::aes_key_setup(key.key, key_schedule, AES_KEY_BITS);
     std::uint8_t input_block[AES_BLOCK_LENGTH];
     std::memcpy(input_block, iv.iv, AES_BLOCK_LENGTH);
     while (input_length >= AES_BLOCK_LENGTH) {
         xor_block<AES_BLOCK_LENGTH>(input_block, input);
-        ::aes_encrypt(input_block, output, key_schedule, 256);
+        ::aes_encrypt(input_block, output, key_schedule, AES_KEY_BITS);
         std::memcpy(input_block, output, AES_BLOCK_LENGTH);
         input += AES_BLOCK_LENGTH;
         output += AES_BLOCK_LENGTH;
@@ -259,7 +260,7 @@ void olm::aes_encrypt_cbc(
     for (; i < AES_BLOCK_LENGTH; ++i) {
         input_block[i] ^= AES_BLOCK_LENGTH - input_length;
     }
-    ::aes_encrypt(input_block, output, key_schedule, 256);
+    ::aes_encrypt(input_block, output, key_schedule, AES_KEY_BITS);
     olm::unset(key_schedule);
     olm::unset(input_block);
 }
@@ -271,14 +272,14 @@ std::size_t olm::aes_decrypt_cbc(
     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::uint32_t key_schedule[AES_KEY_SCHEDULE_LENGTH];
+    ::aes_key_setup(key.key, key_schedule, AES_KEY_BITS);
     std::uint8_t block1[AES_BLOCK_LENGTH];
     std::uint8_t block2[AES_BLOCK_LENGTH];
     std::memcpy(block1, iv.iv, AES_BLOCK_LENGTH);
     for (std::size_t i = 0; i < input_length; i += AES_BLOCK_LENGTH) {
         std::memcpy(block2, &input[i], AES_BLOCK_LENGTH);
-        ::aes_decrypt(&input[i], &output[i], key_schedule, 256);
+        ::aes_decrypt(&input[i], &output[i], key_schedule, AES_KEY_BITS);
         xor_block<AES_BLOCK_LENGTH>(&output[i], block1);
         std::memcpy(block1, block2, AES_BLOCK_LENGTH);
     }
@@ -301,6 +302,7 @@ void olm::sha256(
     olm::unset(context);
 }
 
+
 void olm::hmac_sha256(
     std::uint8_t const * key, std::size_t key_length,
     std::uint8_t const * input, std::size_t input_length,
@@ -325,7 +327,7 @@ void olm::hkdf_sha256(
 ) {
     ::SHA256_CTX context;
     std::uint8_t hmac_key[SHA256_BLOCK_LENGTH];
-    std::uint8_t step_result[SHA256_HASH_LENGTH];
+    std::uint8_t step_result[olm::SHA256_OUTPUT_LENGTH];
     std::size_t bytes_remaining = output_length;
     std::uint8_t iteration = 1;
     if (!salt) {
@@ -337,20 +339,20 @@ void olm::hkdf_sha256(
     hmac_sha256_init(&context, hmac_key);
     ::sha256_update(&context, input, input_length);
     hmac_sha256_final(&context, hmac_key, step_result);
-    hmac_sha256_key(step_result, SHA256_HASH_LENGTH, hmac_key);
+    hmac_sha256_key(step_result, olm::SHA256_OUTPUT_LENGTH, hmac_key);
 
     /* Extract */
     hmac_sha256_init(&context, hmac_key);
     ::sha256_update(&context, info, info_length);
     ::sha256_update(&context, &iteration, 1);
     hmac_sha256_final(&context, hmac_key, step_result);
-    while (bytes_remaining > SHA256_HASH_LENGTH) {
-        std::memcpy(output, step_result, SHA256_HASH_LENGTH);
-        output += SHA256_HASH_LENGTH;
-        bytes_remaining -= SHA256_HASH_LENGTH;
+    while (bytes_remaining > olm::SHA256_OUTPUT_LENGTH) {
+        std::memcpy(output, step_result, olm::SHA256_OUTPUT_LENGTH);
+        output += olm::SHA256_OUTPUT_LENGTH;
+        bytes_remaining -= olm::SHA256_OUTPUT_LENGTH;
         iteration ++;
         hmac_sha256_init(&context, hmac_key);
-        ::sha256_update(&context, step_result, SHA256_HASH_LENGTH);
+        ::sha256_update(&context, step_result, olm::SHA256_OUTPUT_LENGTH);
         ::sha256_update(&context, info, info_length);
         ::sha256_update(&context, &iteration, 1);
         hmac_sha256_final(&context, hmac_key, step_result);
diff --git a/src/olm.cpp b/src/olm.cpp
index 28b194f..63f3d83 100644
--- a/src/olm.cpp
+++ b/src/olm.cpp
@@ -520,8 +520,13 @@ size_t olm_create_outbound_session(
     void const * their_one_time_key, size_t their_one_time_key_length,
     void * random, size_t random_length
 ) {
-    if (olm::decode_base64_length(their_identity_key_length) != 32
-            || olm::decode_base64_length(their_one_time_key_length) != 32
+    std::uint8_t const * id_key = from_c(their_identity_key);
+    std::uint8_t const * ot_key = from_c(their_one_time_key);
+    std::size_t id_key_length = their_identity_key_length;
+    std::size_t ot_key_length = their_one_time_key_length;
+
+    if (olm::decode_base64_length(id_key_length) != olm::KEY_LENGTH
+            || olm::decode_base64_length(ot_key_length) != olm::KEY_LENGTH
     ) {
         from_c(session)->last_error = olm::ErrorCode::INVALID_BASE64;
         return std::size_t(-1);
@@ -529,14 +534,8 @@ size_t olm_create_outbound_session(
     olm::Curve25519PublicKey identity_key;
     olm::Curve25519PublicKey one_time_key;
 
-    olm::decode_base64(
-        from_c(their_identity_key), their_identity_key_length,
-        identity_key.public_key
-    );
-    olm::decode_base64(
-        from_c(their_one_time_key), their_one_time_key_length,
-        one_time_key.public_key
-    );
+    olm::decode_base64(id_key, id_key_length, identity_key.public_key);
+    olm::decode_base64(ot_key, ot_key_length, one_time_key.public_key);
 
     size_t result = from_c(session)->new_outbound_session(
         *from_c(account), identity_key, one_time_key,
@@ -570,15 +569,15 @@ size_t olm_create_inbound_session_from(
     void const * their_identity_key, size_t their_identity_key_length,
     void * one_time_key_message, size_t message_length
 ) {
-    if (olm::decode_base64_length(their_identity_key_length) != 32) {
+    std::uint8_t const * id_key = from_c(their_identity_key);
+    std::size_t id_key_length = their_identity_key_length;
+
+    if (olm::decode_base64_length(id_key_length) != olm::KEY_LENGTH) {
         from_c(session)->last_error = olm::ErrorCode::INVALID_BASE64;
         return std::size_t(-1);
     }
     olm::Curve25519PublicKey identity_key;
-    olm::decode_base64(
-        from_c(their_identity_key), their_identity_key_length,
-        identity_key.public_key
-    );
+    olm::decode_base64(id_key, id_key_length, identity_key.public_key);
 
     std::size_t raw_length = b64_input(
         from_c(one_time_key_message), message_length, from_c(session)->last_error
@@ -641,15 +640,15 @@ size_t olm_matches_inbound_session_from(
     void const * their_identity_key, size_t their_identity_key_length,
     void * one_time_key_message, size_t message_length
 ) {
-    if (olm::decode_base64_length(their_identity_key_length) != 32) {
+    std::uint8_t const * id_key = from_c(their_identity_key);
+    std::size_t id_key_length = their_identity_key_length;
+
+    if (olm::decode_base64_length(id_key_length) != olm::KEY_LENGTH) {
         from_c(session)->last_error = olm::ErrorCode::INVALID_BASE64;
         return std::size_t(-1);
     }
     olm::Curve25519PublicKey identity_key;
-    olm::decode_base64(
-        from_c(their_identity_key), their_identity_key_length,
-        identity_key.public_key
-    );
+    olm::decode_base64(id_key, id_key_length, identity_key.public_key);
 
     std::size_t raw_length = b64_input(
         from_c(one_time_key_message), message_length, from_c(session)->last_error
@@ -800,15 +799,12 @@ size_t olm_ed25519_verify(
     void const * message, size_t message_length,
     void * signature, size_t signature_length
 ) {
-    if (olm::decode_base64_length(key_length) != 32) {
+    if (olm::decode_base64_length(key_length) != olm::KEY_LENGTH) {
         from_c(utility)->last_error = olm::ErrorCode::INVALID_BASE64;
         return std::size_t(-1);
     }
     olm::Ed25519PublicKey verify_key;
-    olm::decode_base64(
-        from_c(key), key_length,
-        verify_key.public_key
-    );
+    olm::decode_base64(from_c(key), key_length, verify_key.public_key);
     std::size_t raw_signature_length = b64_input(
         from_c(signature), signature_length, from_c(utility)->last_error
     );
@@ -822,5 +818,4 @@ size_t olm_ed25519_verify(
     );
 }
 
-
 }
diff --git a/src/ratchet.cpp b/src/ratchet.cpp
index 110ea93..5ef1e56 100644
--- a/src/ratchet.cpp
+++ b/src/ratchet.cpp
@@ -23,11 +23,10 @@
 
 namespace {
 
-std::uint8_t PROTOCOL_VERSION = 3;
-std::size_t KEY_LENGTH = olm::Curve25519PublicKey::LENGTH;
-std::uint8_t MESSAGE_KEY_SEED[1] = {0x01};
-std::uint8_t CHAIN_KEY_SEED[1] = {0x02};
-std::size_t MAX_MESSAGE_GAP = 2000;
+static const std::uint8_t PROTOCOL_VERSION = 3;
+static const std::uint8_t MESSAGE_KEY_SEED[1] = {0x01};
+static const std::uint8_t CHAIN_KEY_SEED[1] = {0x02};
+static const std::size_t MAX_MESSAGE_GAP = 2000;
 
 static void create_chain_key(
     olm::SharedKey const & root_key,
@@ -39,15 +38,16 @@ static void create_chain_key(
 ) {
     olm::SharedKey secret;
     olm::curve25519_shared_secret(our_key, their_key, secret);
-    std::uint8_t derived_secrets[64];
+    std::uint8_t derived_secrets[2 * olm::KEY_LENGTH];
     olm::hkdf_sha256(
         secret, sizeof(secret),
         root_key, sizeof(root_key),
         info.ratchet_info, info.ratchet_info_length,
         derived_secrets, sizeof(derived_secrets)
     );
-    std::memcpy(new_root_key, derived_secrets, 32);
-    std::memcpy(new_chain_key.key, derived_secrets + 32, 32);
+    std::uint8_t const * pos = derived_secrets;
+    pos = olm::load_array(new_root_key, pos);
+    pos = olm::load_array(new_chain_key.key, pos);
     new_chain_key.index = 0;
     olm::unset(derived_secrets);
     olm::unset(secret);
@@ -148,9 +148,7 @@ static std::size_t verify_mac_and_decrypt_for_new_chain(
     if (reader.counter > MAX_MESSAGE_GAP) {
         return std::size_t(-1);
     }
-    std::memcpy(
-        new_chain.ratchet_key.public_key, reader.ratchet_key, KEY_LENGTH
-    );
+    olm::load_array(new_chain.ratchet_key.public_key, reader.ratchet_key);
 
     create_chain_key(
         session.root_key, session.sender_chain[0].ratchet_key,
@@ -183,7 +181,7 @@ void olm::Ratchet::initialise_as_bob(
     std::uint8_t const * shared_secret, std::size_t shared_secret_length,
     olm::Curve25519PublicKey const & their_ratchet_key
 ) {
-    std::uint8_t derived_secrets[64];
+    std::uint8_t derived_secrets[2 * olm::KEY_LENGTH];
     olm::hkdf_sha256(
         shared_secret, shared_secret_length,
         nullptr, 0,
@@ -192,8 +190,9 @@ void olm::Ratchet::initialise_as_bob(
     );
     receiver_chains.insert();
     receiver_chains[0].chain_key.index = 0;
-    std::memcpy(root_key, derived_secrets, 32);
-    std::memcpy(receiver_chains[0].chain_key.key, derived_secrets + 32, 32);
+    std::uint8_t const * pos = derived_secrets;
+    pos = olm::load_array(root_key, pos);
+    pos = olm::load_array(receiver_chains[0].chain_key.key, pos);
     receiver_chains[0].ratchet_key = their_ratchet_key;
     olm::unset(derived_secrets);
 }
@@ -203,7 +202,7 @@ void olm::Ratchet::initialise_as_alice(
     std::uint8_t const * shared_secret, std::size_t shared_secret_length,
     olm::Curve25519KeyPair const & our_ratchet_key
 ) {
-    std::uint8_t derived_secrets[64];
+    std::uint8_t derived_secrets[2 * olm::KEY_LENGTH];
     olm::hkdf_sha256(
         shared_secret, shared_secret_length,
         nullptr, 0,
@@ -212,8 +211,9 @@ void olm::Ratchet::initialise_as_alice(
     );
     sender_chain.insert();
     sender_chain[0].chain_key.index = 0;
-    std::memcpy(root_key, derived_secrets, 32);
-    std::memcpy(sender_chain[0].chain_key.key, derived_secrets + 32, 32);
+    std::uint8_t const * pos = derived_secrets;
+    pos = olm::load_array(root_key, pos);
+    pos = olm::load_array(sender_chain[0].chain_key.key, pos);
     sender_chain[0].ratchet_key = our_ratchet_key;
     olm::unset(derived_secrets);
 }
@@ -224,7 +224,7 @@ namespace olm {
 static std::size_t pickle_length(
     const olm::SharedKey & value
 ) {
-    return KEY_LENGTH;
+    return olm::KEY_LENGTH;
 }
 
 
@@ -232,7 +232,7 @@ static std::uint8_t * pickle(
     std::uint8_t * pos,
     const olm::SharedKey & value
 ) {
-    return olm::pickle_bytes(pos, value, KEY_LENGTH);
+    return olm::pickle_bytes(pos, value, olm::KEY_LENGTH);
 }
 
 
@@ -240,7 +240,7 @@ static std::uint8_t const * unpickle(
     std::uint8_t const * pos, std::uint8_t const * end,
     olm::SharedKey & value
 ) {
-    return olm::unpickle_bytes(pos, end, value, KEY_LENGTH);
+    return olm::unpickle_bytes(pos, end, value, olm::KEY_LENGTH);
 }
 
 
@@ -349,7 +349,7 @@ std::size_t olm::pickle_length(
     olm::Ratchet const & value
 ) {
     std::size_t length = 0;
-    length += KEY_LENGTH;
+    length += olm::KEY_LENGTH;
     length += olm::pickle_length(value.sender_chain);
     length += olm::pickle_length(value.receiver_chains);
     length += olm::pickle_length(value.skipped_message_keys);
@@ -391,13 +391,13 @@ std::size_t olm::Ratchet::encrypt_output_length(
         plaintext_length
     );
     return olm::encode_message_length(
-        counter, KEY_LENGTH, padded, ratchet_cipher.mac_length()
+        counter, olm::KEY_LENGTH, padded, ratchet_cipher.mac_length()
     );
 }
 
 
 std::size_t olm::Ratchet::encrypt_random_length() {
-    return sender_chain.empty() ? KEY_LENGTH : 0;
+    return sender_chain.empty() ? olm::KEY_LENGTH : 0;
 }
 
 
@@ -442,10 +442,11 @@ std::size_t olm::Ratchet::encrypt(
     olm::MessageWriter writer;
 
     olm::encode_message(
-        writer, PROTOCOL_VERSION, counter, KEY_LENGTH, ciphertext_length, output
+        writer, PROTOCOL_VERSION, counter, olm::KEY_LENGTH, ciphertext_length,
+        output
     );
 
-    std::memcpy(writer.ratchet_key, ratchet_key.public_key, KEY_LENGTH);
+    olm::store_array(writer.ratchet_key, ratchet_key.public_key);
 
     ratchet_cipher.encrypt(
         keys.key, sizeof(keys.key),
@@ -504,7 +505,7 @@ std::size_t olm::Ratchet::decrypt(
         return std::size_t(-1);
     }
 
-    if (reader.ratchet_key_length != KEY_LENGTH) {
+    if (reader.ratchet_key_length != olm::KEY_LENGTH) {
         last_error = olm::ErrorCode::BAD_MESSAGE_FORMAT;
         return std::size_t(-1);
     }
@@ -513,7 +514,7 @@ std::size_t olm::Ratchet::decrypt(
     for (olm::ReceiverChain & receiver_chain : receiver_chains) {
         if (0 == std::memcmp(
                 receiver_chain.ratchet_key.public_key, reader.ratchet_key,
-                KEY_LENGTH
+                olm::KEY_LENGTH
         )) {
             chain = &receiver_chain;
             break;
@@ -533,7 +534,7 @@ std::size_t olm::Ratchet::decrypt(
             if (reader.counter == skipped.message_key.index
                     && 0 == std::memcmp(
                         skipped.ratchet_key.public_key, reader.ratchet_key,
-                        KEY_LENGTH
+                        olm::KEY_LENGTH
                     )
             ) {
                 /* Found the key for this message. Check the MAC. */
@@ -569,9 +570,7 @@ std::size_t olm::Ratchet::decrypt(
          * We can discard our previous empheral ratchet key.
          * We will generate a new key when we send the next message. */
         chain = receiver_chains.insert();
-        std::memcpy(
-            chain->ratchet_key.public_key, reader.ratchet_key, KEY_LENGTH
-        );
+        olm::load_array(chain->ratchet_key.public_key, reader.ratchet_key);
         create_chain_key(
             root_key, sender_chain[0].ratchet_key, chain->ratchet_key,
             kdf_info, root_key, chain->chain_key
diff --git a/src/session.cpp b/src/session.cpp
index 18f0000..71c80e4 100644
--- a/src/session.cpp
+++ b/src/session.cpp
@@ -24,7 +24,6 @@
 
 namespace {
 
-static const std::size_t KEY_LENGTH = 32;
 static const std::uint8_t PROTOCOL_VERSION = 0x3;
 
 static const std::uint8_t ROOT_KDF_INFO[] = "OLM_ROOT";
@@ -51,7 +50,7 @@ olm::Session::Session(
 
 
 std::size_t olm::Session::new_outbound_session_random_length() {
-    return KEY_LENGTH * 2;
+    return olm::KEY_LENGTH * 2;
 }
 
 
@@ -66,35 +65,35 @@ std::size_t olm::Session::new_outbound_session(
         return std::size_t(-1);
     }
 
-    Curve25519KeyPair base_key;
+    olm::Curve25519KeyPair base_key;
     olm::curve25519_generate_key(random, base_key);
 
-    Curve25519KeyPair ratchet_key;
-    olm::curve25519_generate_key(random + 32, ratchet_key);
+    olm::Curve25519KeyPair ratchet_key;
+    olm::curve25519_generate_key(random + olm::KEY_LENGTH, ratchet_key);
+
+    olm::Curve25519KeyPair const & alice_identity_key_pair = (
+        local_account.identity_keys.curve25519_key
+    );
 
     received_message = false;
-    alice_identity_key = local_account.identity_keys.curve25519_key;
+    alice_identity_key = alice_identity_key_pair;
     alice_base_key = base_key;
     bob_one_time_key = one_time_key;
 
-    std::uint8_t shared_secret[96];
+    std::uint8_t secret[3 * olm::KEY_LENGTH];
+    std::uint8_t * pos = secret;
 
-    olm::curve25519_shared_secret(
-        local_account.identity_keys.curve25519_key,
-        one_time_key, shared_secret
-    );
-    olm::curve25519_shared_secret(
-         base_key, identity_key, shared_secret + 32
-    );
-    olm::curve25519_shared_secret(
-         base_key, one_time_key, shared_secret + 64
-    );
+    olm::curve25519_shared_secret(alice_identity_key_pair, one_time_key, pos);
+    pos += olm::KEY_LENGTH;
+    olm::curve25519_shared_secret(base_key, identity_key, pos);
+    pos += olm::KEY_LENGTH;
+    olm::curve25519_shared_secret(base_key, one_time_key, pos);
 
-    ratchet.initialise_as_alice(shared_secret, 96, ratchet_key);
+    ratchet.initialise_as_alice(secret, sizeof(secret), ratchet_key);
 
     olm::unset(base_key);
     olm::unset(ratchet_key);
-    olm::unset(shared_secret);
+    olm::unset(secret);
 
     return std::size_t(0);
 }
@@ -107,13 +106,13 @@ static bool check_message_fields(
     bool ok = true;
     ok = ok && (have_their_identity_key || reader.identity_key);
     if (reader.identity_key) {
-        ok = ok && reader.identity_key_length == KEY_LENGTH;
+        ok = ok && reader.identity_key_length == olm::KEY_LENGTH;
     }
     ok = ok && reader.message;
     ok = ok && reader.base_key;
-    ok = ok && reader.base_key_length == KEY_LENGTH;
+    ok = ok && reader.base_key_length == olm::KEY_LENGTH;
     ok = ok && reader.one_time_key;
-    ok = ok && reader.one_time_key_length == KEY_LENGTH;
+    ok = ok && reader.one_time_key_length == olm::KEY_LENGTH;
     return ok;
 }
 
@@ -135,7 +134,7 @@ std::size_t olm::Session::new_inbound_session(
 
     if (reader.identity_key && their_identity_key) {
         bool same = 0 == std::memcmp(
-            their_identity_key->public_key, reader.identity_key, KEY_LENGTH
+            their_identity_key->public_key, reader.identity_key, olm::KEY_LENGTH
         );
         if (!same) {
             last_error = olm::ErrorCode::BAD_MESSAGE_KEY_ID;
@@ -150,16 +149,16 @@ std::size_t olm::Session::new_inbound_session(
     );
 
     if (!message_reader.ratchet_key
-            || message_reader.ratchet_key_length != KEY_LENGTH) {
+            || message_reader.ratchet_key_length != olm::KEY_LENGTH) {
         last_error = olm::ErrorCode::BAD_MESSAGE_FORMAT;
         return std::size_t(-1);
     }
 
-    std::memcpy(alice_identity_key.public_key, reader.identity_key, 32);
-    std::memcpy(alice_base_key.public_key, reader.base_key, 32);
-    std::memcpy(bob_one_time_key.public_key, reader.one_time_key, 32);
+    olm::load_array(alice_identity_key.public_key, reader.identity_key);
+    olm::load_array(alice_base_key.public_key, reader.base_key);
+    olm::load_array(bob_one_time_key.public_key, reader.one_time_key);
     olm::Curve25519PublicKey ratchet_key;
-    std::memcpy(ratchet_key.public_key, message_reader.ratchet_key, 32);
+    olm::load_array(ratchet_key.public_key, message_reader.ratchet_key);
 
     olm::OneTimeKey const * our_one_time_key = local_account.lookup_key(
         bob_one_time_key
@@ -170,27 +169,28 @@ std::size_t olm::Session::new_inbound_session(
         return std::size_t(-1);
     }
 
-    std::uint8_t shared_secret[96];
-
-    olm::curve25519_shared_secret(
-        our_one_time_key->key, alice_identity_key, shared_secret
-    );
-    olm::curve25519_shared_secret(
-        local_account.identity_keys.curve25519_key,
-        alice_base_key, shared_secret + 32
-    );
-    olm::curve25519_shared_secret(
-        our_one_time_key->key, alice_base_key, shared_secret + 64
+    olm::Curve25519KeyPair const & bob_identity_key = (
+        local_account.identity_keys.curve25519_key
     );
+    olm::Curve25519KeyPair const & bob_one_time_key = our_one_time_key->key;
+
+    std::uint8_t secret[olm::KEY_LENGTH * 3];
+    std::uint8_t * pos = secret;
+    olm::curve25519_shared_secret(bob_one_time_key, alice_identity_key, pos);
+    pos += olm::KEY_LENGTH;
+    olm::curve25519_shared_secret(bob_identity_key, alice_base_key, pos);
+    pos += olm::KEY_LENGTH;
+    olm::curve25519_shared_secret(bob_one_time_key, alice_base_key, pos);
 
-    ratchet.initialise_as_bob(shared_secret, 96, ratchet_key);
+    ratchet.initialise_as_bob(secret, sizeof(secret), ratchet_key);
 
+    olm::unset(secret);
     return std::size_t(0);
 }
 
 
 std::size_t olm::Session::session_id_length() {
-    return 32;
+    return olm::SHA256_OUTPUT_LENGTH;
 }
 
 
@@ -201,10 +201,11 @@ std::size_t olm::Session::session_id(
         last_error = olm::ErrorCode::OUTPUT_BUFFER_TOO_SMALL;
         return std::size_t(-1);
     }
-    std::uint8_t tmp[96];
-    std::memcpy(tmp, alice_identity_key.public_key, 32);
-    std::memcpy(tmp + 32, alice_base_key.public_key, 32);
-    std::memcpy(tmp + 64, bob_one_time_key.public_key, 32);
+    std::uint8_t tmp[olm::KEY_LENGTH * 3];
+    std::uint8_t * pos = tmp;
+    pos = olm::store_array(pos, alice_identity_key.public_key);
+    pos = olm::store_array(pos, alice_base_key.public_key);
+    pos = olm::store_array(pos, bob_one_time_key.public_key);
     olm::sha256(tmp, sizeof(tmp), id);
     return session_id_length();
 }
@@ -224,20 +225,20 @@ bool olm::Session::matches_inbound_session(
     bool same = true;
     if (reader.identity_key) {
         same = same && 0 == std::memcmp(
-            reader.identity_key, alice_identity_key.public_key, KEY_LENGTH
+            reader.identity_key, alice_identity_key.public_key, olm::KEY_LENGTH
         );
     }
     if (their_identity_key) {
         same = same && 0 == std::memcmp(
             their_identity_key->public_key, alice_identity_key.public_key,
-            KEY_LENGTH
+            olm::KEY_LENGTH
         );
     }
     same = same && 0 == std::memcmp(
-        reader.base_key, alice_base_key.public_key, KEY_LENGTH
+        reader.base_key, alice_base_key.public_key, olm::KEY_LENGTH
     );
     same = same && 0 == std::memcmp(
-        reader.one_time_key, bob_one_time_key.public_key, KEY_LENGTH
+        reader.one_time_key, bob_one_time_key.public_key, olm::KEY_LENGTH
     );
     return same;
 }
@@ -264,9 +265,9 @@ std::size_t olm::Session::encrypt_message_length(
     }
 
     return encode_one_time_key_message_length(
-        KEY_LENGTH,
-        KEY_LENGTH,
-        KEY_LENGTH,
+        olm::KEY_LENGTH,
+        olm::KEY_LENGTH,
+        olm::KEY_LENGTH,
         message_length
     );
 }
@@ -298,21 +299,15 @@ std::size_t olm::Session::encrypt(
         encode_one_time_key_message(
             writer,
             PROTOCOL_VERSION,
-            KEY_LENGTH,
-            KEY_LENGTH,
-            KEY_LENGTH,
+            olm::KEY_LENGTH,
+            olm::KEY_LENGTH,
+            olm::KEY_LENGTH,
             message_body_length,
             message
         );
-        std::memcpy(
-            writer.one_time_key, bob_one_time_key.public_key, KEY_LENGTH
-        );
-        std::memcpy(
-            writer.identity_key, alice_identity_key.public_key, KEY_LENGTH
-        );
-        std::memcpy(
-            writer.base_key, alice_base_key.public_key, KEY_LENGTH
-        );
+        olm::store_array(writer.one_time_key, bob_one_time_key.public_key);
+        olm::store_array(writer.identity_key, alice_identity_key.public_key);
+        olm::store_array(writer.base_key, alice_base_key.public_key);
         message_body = writer.message;
     }
 
diff --git a/src/utility.cpp b/src/utility.cpp
index 1d8c5c1..bc51cff 100644
--- a/src/utility.cpp
+++ b/src/utility.cpp
@@ -23,7 +23,7 @@ olm::Utility::Utility(
 
 
 size_t olm::Utility::sha256_length() {
-    return olm::HMAC_SHA256_OUTPUT_LENGTH;
+    return olm::SHA256_OUTPUT_LENGTH;
 }
 
 
@@ -36,7 +36,7 @@ size_t olm::Utility::sha256(
         return std::size_t(-1);
     }
     olm::sha256(input, input_length, output);
-    return 32;
+    return olm::SHA256_OUTPUT_LENGTH;
 }
 
 
@@ -45,7 +45,7 @@ size_t olm::Utility::ed25519_verify(
     std::uint8_t const * message, std::size_t message_length,
     std::uint8_t const * signature, std::size_t signature_length
 ) {
-    if (signature_length < 64) {
+    if (signature_length < olm::SIGNATURE_LENGTH) {
         last_error = olm::ErrorCode::BAD_MESSAGE_MAC;
         return std::size_t(-1);
     }
diff --git a/tests/test_base64.cpp b/tests/test_base64.cpp
index e6b3710..5bae2f9 100644
--- a/tests/test_base64.cpp
+++ b/tests/test_base64.cpp
@@ -33,5 +33,4 @@ olm::decode_base64(input, input_length, output);
 assert_equals(expected_output, output, output_length);
 }
 
-
 }
diff --git a/tests/test_crypto.cpp b/tests/test_crypto.cpp
index b3ff593..4606c52 100644
--- a/tests/test_crypto.cpp
+++ b/tests/test_crypto.cpp
@@ -70,7 +70,7 @@ olm::curve25519_generate_key(bob_private, bob_pair);
 assert_equals(bob_private, bob_pair.private_key, 32);
 assert_equals(bob_public, bob_pair.public_key, 32);
 
-std::uint8_t actual_agreement[olm::CURVE25519_SHARED_SECRET_LENGTH] = {};
+std::uint8_t actual_agreement[olm::KEY_LENGTH] = {};
 
 olm::curve25519_shared_secret(alice_pair, bob_pair, actual_agreement);