1 files changed, 74 insertions, 15 deletions

diff --git a/src/lilliput-ae-ii.c b/src/lilliput-ae-ii.c
index fc50211..e0e268e 100644
--- a/src/lilliput-ae-ii.c
+++ b/src/lilliput-ae-ii.c
@@ -7,16 +7,62 @@
 #include "lilliput-ae.h"
 
 
+static void _init_msg_tweak(const uint8_t tag[TAG_BYTES], uint8_t tweak[TWEAK_BYTES])
+{
+    /* The t-bit tweak is filled as follows:
+     *
+     * - bits [  1, t-1]: tag + block index
+     *        [  1,  64]: tag[ 1.. 64] XOR block index
+     *        [ 65, t-1]: tag[65..t-1]
+     * - bit t: 1
+     */
+
+    memcpy(tweak+sizeof(uint64_t), tag+sizeof(uint64_t), TAG_BYTES-sizeof(uint64_t));
+    tweak[TWEAK_BYTES-1] |= 0x80;
+}
+
+static void _fill_msg_tweak(const uint8_t tag[TAG_BYTES], uint64_t block_index, uint8_t tweak[TWEAK_BYTES])
+{
+    /* Assume bits 65 to t-1 are set. */
+    for (size_t i=0; i<sizeof(block_index); i++)
+    {
+        uint8_t index_i = block_index >> i*8 & 0xff;
+        tweak[i] = tag[i] ^ index_i;
+    }
+}
 
 static void _generate_tag(
     const uint8_t key[KEY_BYTES],
     size_t        M_len,
     const uint8_t M[M_len],
-    const uint8_t N[NONCE_BYTES],
     const uint8_t Auth[BLOCK_BYTES],
     uint8_t       tag[TAG_BYTES]
 )
 {
+    uint8_t Ek_Mj[BLOCK_BYTES];
+    uint8_t tweak[TWEAK_BYTES];
+    memset(tweak, 0, TWEAK_BYTES);
+
+    memcpy(tag, Auth, TAG_BYTES);
+
+    size_t l = M_len / BLOCK_BYTES;
+    size_t rest = M_len % BLOCK_BYTES;
+
+    for (size_t j=0; j<l; j++)
+    {
+        fill_index_tweak(0x0, j, tweak);
+        encrypt(key, tweak, &M[j*BLOCK_BYTES], Ek_Mj);
+        xor_into(tag, Ek_Mj);
+    }
+
+    if (rest != 0)
+    {
+        uint8_t M_rest[BLOCK_BYTES];
+        pad10(rest, &M[l*BLOCK_BYTES], M_rest);
+        fill_index_tweak(0x4, l, tweak);
+        encrypt(key, tweak, M_rest, Ek_Mj);
+        xor_into(tag, Ek_Mj);
+    }
 }
 
 static void _encrypt_message(
@@ -28,19 +74,32 @@ static void _encrypt_message(
     uint8_t       C[M_len]
 )
 {
-}
+    uint8_t Ek_N[BLOCK_BYTES];
 
-static void _decrypt_message(
-    const uint8_t key[KEY_BYTES],
-    size_t C_len,
-    const uint8_t C[C_len],
-    const uint8_t N[NONCE_BYTES],
-    const uint8_t tag[TAG_BYTES],
-    uint8_t       M[C_len]
-)
-{
-}
+    uint8_t tweak[TWEAK_BYTES];
+    _init_msg_tweak(tag, tweak);
+
+    uint8_t padded_N[BLOCK_BYTES];
+    memcpy(padded_N, N, NONCE_BYTES);
+    padded_N[BLOCK_BYTES-1] = 0;
+
+    size_t l = M_len / BLOCK_BYTES;
+    size_t rest = M_len % BLOCK_BYTES;
 
+    for (size_t j=0; j<l; j++)
+    {
+        _fill_msg_tweak(tag, j, tweak);
+        encrypt(key, tweak, padded_N, Ek_N);
+        xor_arrays(BLOCK_BYTES, &C[j*BLOCK_BYTES], &M[j*BLOCK_BYTES], Ek_N);
+    }
+
+    if (rest != 0)
+    {
+        _fill_msg_tweak(tag, l, tweak);
+        encrypt(key, tweak, padded_N, Ek_N);
+        xor_arrays(rest, &C[l*BLOCK_BYTES], &M[l*BLOCK_BYTES], Ek_N);
+    }
+}
 
 void lilliput_ae_encrypt(
     size_t        message_len,
@@ -56,7 +115,7 @@ void lilliput_ae_encrypt(
     uint8_t auth[BLOCK_BYTES];
     process_associated_data(key, auth_data_len, auth_data, auth);
 
-    _generate_tag(key, message_len, message, nonce, auth, tag);
+    _generate_tag(key, message_len, message, auth, tag);
 
     _encrypt_message(key, message_len, message, nonce, tag, ciphertext);
 }
@@ -72,13 +131,13 @@ bool lilliput_ae_decrypt(
     uint8_t       message[ciphertext_len]
 )
 {
-    _decrypt_message(key, ciphertext_len, ciphertext, nonce, tag, message);
+    _encrypt_message(key, ciphertext_len, ciphertext, nonce, tag, message);
 
     uint8_t auth[BLOCK_BYTES];
     process_associated_data(key, auth_data_len, auth_data, auth);
 
     uint8_t effective_tag[TAG_BYTES];
-    _generate_tag(key, ciphertext_len, message, nonce, auth, effective_tag);
+    _generate_tag(key, ciphertext_len, message, auth, effective_tag);
 
     return memcmp(tag, effective_tag, TAG_BYTES) == 0;
 }