crypto: add additional query accessors for cipher instances

Adds new methods to allow querying the length of the cipher
key, block size and initialization vectors.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

crypto/cipher.c

@@ -28,6 +28,54 @@ static size_t alg_key_len[QCRYPTO_CIPHER_ALG_LAST] = {
     [QCRYPTO_CIPHER_ALG_DES_RFB] = 8,
 };
 
+static size_t alg_block_len[QCRYPTO_CIPHER_ALG_LAST] = {
+    [QCRYPTO_CIPHER_ALG_AES_128] = 16,
+    [QCRYPTO_CIPHER_ALG_AES_192] = 16,
+    [QCRYPTO_CIPHER_ALG_AES_256] = 16,
+    [QCRYPTO_CIPHER_ALG_DES_RFB] = 8,
+};
+
+static bool mode_need_iv[QCRYPTO_CIPHER_MODE_LAST] = {
+    [QCRYPTO_CIPHER_MODE_ECB] = false,
+    [QCRYPTO_CIPHER_MODE_CBC] = true,
+};
+
+
+size_t qcrypto_cipher_get_block_len(QCryptoCipherAlgorithm alg)
+{
+    if (alg >= G_N_ELEMENTS(alg_key_len)) {
+        return 0;
+    }
+    return alg_block_len[alg];
+}
+
+
+size_t qcrypto_cipher_get_key_len(QCryptoCipherAlgorithm alg)
+{
+    if (alg >= G_N_ELEMENTS(alg_key_len)) {
+        return 0;
+    }
+    return alg_key_len[alg];
+}
+
+
+size_t qcrypto_cipher_get_iv_len(QCryptoCipherAlgorithm alg,
+                                 QCryptoCipherMode mode)
+{
+    if (alg >= G_N_ELEMENTS(alg_block_len)) {
+        return 0;
+    }
+    if (mode >= G_N_ELEMENTS(mode_need_iv)) {
+        return 0;
+    }
+
+    if (mode_need_iv[mode]) {
+        return alg_block_len[alg];
+    }
+    return 0;
+}
+
+
 static bool
 qcrypto_cipher_validate_key_length(QCryptoCipherAlgorithm alg,
                                    size_t nkey,

include/crypto/cipher.h

@@ -107,6 +107,43 @@ struct QCryptoCipher {
  */
 bool qcrypto_cipher_supports(QCryptoCipherAlgorithm alg);
 
+/**
+ * qcrypto_cipher_get_block_len:
+ * @alg: the cipher algorithm
+ *
+ * Get the required data block size in bytes. When
+ * encrypting data, it must be a multiple of the
+ * block size.
+ *
+ * Returns: the block size in bytes
+ */
+size_t qcrypto_cipher_get_block_len(QCryptoCipherAlgorithm alg);
+
+
+/**
+ * qcrypto_cipher_get_key_len:
+ * @alg: the cipher algorithm
+ *
+ * Get the required key size in bytes.
+ *
+ * Returns: the key size in bytes
+ */
+size_t qcrypto_cipher_get_key_len(QCryptoCipherAlgorithm alg);
+
+
+/**
+ * qcrypto_cipher_get_iv_len:
+ * @alg: the cipher algorithm
+ * @mode: the cipher mode
+ *
+ * Get the required initialization vector size
+ * in bytes, if one is required.
+ *
+ * Returns: the IV size in bytes, or 0 if no IV is permitted
+ */
+size_t qcrypto_cipher_get_iv_len(QCryptoCipherAlgorithm alg,
+                                 QCryptoCipherMode mode);
+
 
 /**
  * qcrypto_cipher_new:

tests/test-crypto-cipher.c

@@ -229,6 +229,7 @@ static void test_cipher(const void *opaque)
     uint8_t *key, *iv, *ciphertext, *plaintext, *outtext;
     size_t nkey, niv, nciphertext, nplaintext;
     char *outtexthex;
+    size_t ivsize, keysize, blocksize;
 
     nkey = unhex_string(data->key, &key);
     niv = unhex_string(data->iv, &iv);
@@ -245,6 +246,15 @@ static void test_cipher(const void *opaque)
         &error_abort);
     g_assert(cipher != NULL);
 
+    keysize = qcrypto_cipher_get_key_len(data->alg);
+    blocksize = qcrypto_cipher_get_block_len(data->alg);
+    ivsize = qcrypto_cipher_get_iv_len(data->alg, data->mode);
+
+    g_assert_cmpint(keysize, ==, nkey);
+    g_assert_cmpint(ivsize, ==, niv);
+    if (niv) {
+        g_assert_cmpint(blocksize, ==, niv);
+    }
 
     if (iv) {
         g_assert(qcrypto_cipher_setiv(cipher,