crypto: wire up XTS mode for cipher APIs

Introduce 'XTS' as a permitted mode for the cipher APIs.
With XTS the key provided must be twice the size of the
key normally required for any given algorithm. This is
because the key will be split into two pieces for use
in XTS mode.

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

1 files changed, 23 insertions, 4 deletions

diff --git a/crypto/cipher.c b/crypto/cipher.c
index 89fa5a2c70..5402d18525 100644
--- a/crypto/cipher.c
+++ b/crypto/cipher.c
@@ -53,6 +53,7 @@ static size_t alg_block_len[QCRYPTO_CIPHER_ALG__MAX] = {
 static bool mode_need_iv[QCRYPTO_CIPHER_MODE__MAX] = {
     [QCRYPTO_CIPHER_MODE_ECB] = false,
     [QCRYPTO_CIPHER_MODE_CBC] = true,
+    [QCRYPTO_CIPHER_MODE_XTS] = true,
 };
 
 
@@ -93,6 +94,7 @@ size_t qcrypto_cipher_get_iv_len(QCryptoCipherAlgorithm alg,
 
 static bool
 qcrypto_cipher_validate_key_length(QCryptoCipherAlgorithm alg,
+                                   QCryptoCipherMode mode,
                                    size_t nkey,
                                    Error **errp)
 {
@@ -102,10 +104,27 @@ qcrypto_cipher_validate_key_length(QCryptoCipherAlgorithm alg,
         return false;
     }
 
-    if (alg_key_len[alg] != nkey) {
-        error_setg(errp, "Cipher key length %zu should be %zu",
-                   nkey, alg_key_len[alg]);
-        return false;
+    if (mode == QCRYPTO_CIPHER_MODE_XTS) {
+        if (alg == QCRYPTO_CIPHER_ALG_DES_RFB) {
+            error_setg(errp, "XTS mode not compatible with DES-RFB");
+            return false;
+        }
+        if (nkey % 2) {
+            error_setg(errp, "XTS cipher key length should be a multiple of 2");
+            return false;
+        }
+
+        if (alg_key_len[alg] != (nkey / 2)) {
+            error_setg(errp, "Cipher key length %zu should be %zu",
+                       nkey, alg_key_len[alg] * 2);
+            return false;
+        }
+    } else {
+        if (alg_key_len[alg] != nkey) {
+            error_setg(errp, "Cipher key length %zu should be %zu",
+                       nkey, alg_key_len[alg]);
+            return false;
+        }
     }
     return true;
 }