Switch to CTR instead of CBC mode for encryption.

This should handle arbitrarily messages better.  Later we ought to switch
to something like EAX, so consider this change temporary.

diff --git a/bluesky/crypto.c b/bluesky/crypto.c
index 4490e8c..5b22357 100644 (file)
--- a/bluesky/crypto.c
+++ b/bluesky/crypto.c
@@ -20,6 +20,8 @@
  * the functions in this file, so this is the only point where we interface
  * with an external cryptographic library. */
 
+/* TODO: We ought to switch to an authenticated encryption mode like EAX. */
+
 GCRY_THREAD_OPTION_PTHREAD_IMPL;
 
 void bluesky_crypt_init()
@@ -64,8 +66,8 @@ BlueSkyRCStr *bluesky_crypt_encrypt(BlueSkyRCStr *in, const uint8_t *key)
     gcry_error_t status;
     gcry_cipher_hd_t handle;
 
-    status = gcry_cipher_open(&handle, GCRY_CIPHER_AES, GCRY_CIPHER_MODE_CBC,
-                              GCRY_CIPHER_CBC_CTS);
+    status = gcry_cipher_open(&handle, GCRY_CIPHER_AES, GCRY_CIPHER_MODE_CTR,
+                              0);
     if (status) {
         g_error("gcrypt error setting up encryption: %s\n",
                 gcry_strerror(status));
@@ -80,7 +82,7 @@ BlueSkyRCStr *bluesky_crypt_encrypt(BlueSkyRCStr *in, const uint8_t *key)
     }
 
     bluesky_crypt_random_bytes(out, CRYPTO_BLOCK_SIZE);
-    status = gcry_cipher_setiv(handle, out, CRYPTO_BLOCK_SIZE);
+    status = gcry_cipher_setctr(handle, out, CRYPTO_BLOCK_SIZE);
     if (status) {
         g_error("gcrypt error setting IV: %s\n",
                 gcry_strerror(status));
@@ -106,8 +108,8 @@ BlueSkyRCStr *bluesky_crypt_decrypt(BlueSkyRCStr *in, const uint8_t *key)
 
     g_return_val_if_fail(in->len > CRYPTO_BLOCK_SIZE, NULL);
 
-    status = gcry_cipher_open(&handle, GCRY_CIPHER_AES, GCRY_CIPHER_MODE_CBC,
-                              GCRY_CIPHER_CBC_CTS);
+    status = gcry_cipher_open(&handle, GCRY_CIPHER_AES, GCRY_CIPHER_MODE_CTR,
+                              0);
     if (status) {
         g_error("gcrypt error setting up encryption: %s\n",
                 gcry_strerror(status));
@@ -121,7 +123,7 @@ BlueSkyRCStr *bluesky_crypt_decrypt(BlueSkyRCStr *in, const uint8_t *key)
                 gcry_strerror(status));
     }
 
-    status = gcry_cipher_setiv(handle, in->data, CRYPTO_BLOCK_SIZE);
+    status = gcry_cipher_setctr(handle, in->data, CRYPTO_BLOCK_SIZE);
     if (status) {
         g_error("gcrypt error setting IV: %s\n",
                 gcry_strerror(status));