+
+/* Decrypt a data block. */
+BlueSkyRCStr *bluesky_crypt_decrypt(BlueSkyRCStr *in, const uint8_t *key)
+{
+ gcry_error_t status;
+ gcry_cipher_hd_t handle;
+
+ g_return_val_if_fail(in->len > CRYPTO_BLOCK_SIZE, NULL);
+
+ 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));
+ }
+
+ uint8_t *out = g_malloc0(in->len - CRYPTO_BLOCK_SIZE);
+
+ gcry_cipher_setkey(handle, key, CRYPTO_KEY_SIZE);
+ if (status) {
+ g_error("gcrypt error setting key: %s\n",
+ gcry_strerror(status));
+ }
+
+ status = gcry_cipher_setctr(handle, in->data, CRYPTO_BLOCK_SIZE);
+ if (status) {
+ g_error("gcrypt error setting IV: %s\n",
+ gcry_strerror(status));
+ }
+
+ status = gcry_cipher_decrypt(handle, out, in->len - CRYPTO_BLOCK_SIZE,
+ in->data + CRYPTO_BLOCK_SIZE,
+ in->len - CRYPTO_BLOCK_SIZE);
+ if (status) {
+ g_error("gcrypt error decrypting: %s\n",
+ gcry_strerror(status));
+ }
+
+ gcry_cipher_close(handle);
+
+ return bluesky_string_new(out, in->len - CRYPTO_BLOCK_SIZE);
+}