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, 76 insertions, 9 deletions

diff --git a/crypto/cipher-builtin.c b/crypto/cipher-builtin.c
index 836ed1a..88963f6 100644
--- a/crypto/cipher-builtin.c
+++ b/crypto/cipher-builtin.c
@@ -21,6 +21,7 @@
 #include "qemu/osdep.h"
 #include "crypto/aes.h"
 #include "crypto/desrfb.h"
+#include "crypto/xts.h"
 
 typedef struct QCryptoCipherBuiltinAESContext QCryptoCipherBuiltinAESContext;
 struct QCryptoCipherBuiltinAESContext {
@@ -30,6 +31,7 @@ struct QCryptoCipherBuiltinAESContext {
 typedef struct QCryptoCipherBuiltinAES QCryptoCipherBuiltinAES;
 struct QCryptoCipherBuiltinAES {
     QCryptoCipherBuiltinAESContext key;
+    QCryptoCipherBuiltinAESContext key_tweak;
     uint8_t iv[AES_BLOCK_SIZE];
 };
 typedef struct QCryptoCipherBuiltinDESRFB QCryptoCipherBuiltinDESRFB;
@@ -123,6 +125,30 @@ static void qcrypto_cipher_aes_ecb_decrypt(AES_KEY *key,
 }
 
 
+static void qcrypto_cipher_aes_xts_encrypt(const void *ctx,
+                                           size_t length,
+                                           uint8_t *dst,
+                                           const uint8_t *src)
+{
+    const QCryptoCipherBuiltinAESContext *aesctx = ctx;
+
+    qcrypto_cipher_aes_ecb_encrypt((AES_KEY *)&aesctx->enc,
+                                   src, dst, length);
+}
+
+
+static void qcrypto_cipher_aes_xts_decrypt(const void *ctx,
+                                           size_t length,
+                                           uint8_t *dst,
+                                           const uint8_t *src)
+{
+    const QCryptoCipherBuiltinAESContext *aesctx = ctx;
+
+    qcrypto_cipher_aes_ecb_decrypt((AES_KEY *)&aesctx->dec,
+                                   src, dst, length);
+}
+
+
 static int qcrypto_cipher_encrypt_aes(QCryptoCipher *cipher,
                                       const void *in,
                                       void *out,
@@ -141,6 +167,14 @@ static int qcrypto_cipher_encrypt_aes(QCryptoCipher *cipher,
                         &ctxt->state.aes.key.enc,
                         ctxt->state.aes.iv, 1);
         break;
+    case QCRYPTO_CIPHER_MODE_XTS:
+        xts_encrypt(&ctxt->state.aes.key,
+                    &ctxt->state.aes.key_tweak,
+                    qcrypto_cipher_aes_xts_encrypt,
+                    qcrypto_cipher_aes_xts_decrypt,
+                    ctxt->state.aes.iv,
+                    len, out, in);
+        break;
     default:
         g_assert_not_reached();
     }
@@ -167,6 +201,14 @@ static int qcrypto_cipher_decrypt_aes(QCryptoCipher *cipher,
                         &ctxt->state.aes.key.dec,
                         ctxt->state.aes.iv, 0);
         break;
+    case QCRYPTO_CIPHER_MODE_XTS:
+        xts_decrypt(&ctxt->state.aes.key,
+                    &ctxt->state.aes.key_tweak,
+                    qcrypto_cipher_aes_xts_encrypt,
+                    qcrypto_cipher_aes_xts_decrypt,
+                    ctxt->state.aes.iv,
+                    len, out, in);
+        break;
     default:
         g_assert_not_reached();
     }
@@ -200,21 +242,46 @@ static int qcrypto_cipher_init_aes(QCryptoCipher *cipher,
     QCryptoCipherBuiltin *ctxt;
 
     if (cipher->mode != QCRYPTO_CIPHER_MODE_CBC &&
-        cipher->mode != QCRYPTO_CIPHER_MODE_ECB) {
+        cipher->mode != QCRYPTO_CIPHER_MODE_ECB &&
+        cipher->mode != QCRYPTO_CIPHER_MODE_XTS) {
         error_setg(errp, "Unsupported cipher mode %d", cipher->mode);
         return -1;
     }
 
     ctxt = g_new0(QCryptoCipherBuiltin, 1);
 
-    if (AES_set_encrypt_key(key, nkey * 8, &ctxt->state.aes.key.enc) != 0) {
-        error_setg(errp, "Failed to set encryption key");
-        goto error;
-    }
+    if (cipher->mode == QCRYPTO_CIPHER_MODE_XTS) {
+        if (AES_set_encrypt_key(key, nkey * 4, &ctxt->state.aes.key.enc) != 0) {
+            error_setg(errp, "Failed to set encryption key");
+            goto error;
+        }
 
-    if (AES_set_decrypt_key(key, nkey * 8, &ctxt->state.aes.key.dec) != 0) {
-        error_setg(errp, "Failed to set decryption key");
-        goto error;
+        if (AES_set_decrypt_key(key, nkey * 4, &ctxt->state.aes.key.dec) != 0) {
+            error_setg(errp, "Failed to set decryption key");
+            goto error;
+        }
+
+        if (AES_set_encrypt_key(key + (nkey / 2), nkey * 4,
+                                &ctxt->state.aes.key_tweak.enc) != 0) {
+            error_setg(errp, "Failed to set encryption key");
+            goto error;
+        }
+
+        if (AES_set_decrypt_key(key + (nkey / 2), nkey * 4,
+                                &ctxt->state.aes.key_tweak.dec) != 0) {
+            error_setg(errp, "Failed to set decryption key");
+            goto error;
+        }
+    } else {
+        if (AES_set_encrypt_key(key, nkey * 8, &ctxt->state.aes.key.enc) != 0) {
+            error_setg(errp, "Failed to set encryption key");
+            goto error;
+        }
+
+        if (AES_set_decrypt_key(key, nkey * 8, &ctxt->state.aes.key.dec) != 0) {
+            error_setg(errp, "Failed to set decryption key");
+            goto error;
+        }
     }
 
     ctxt->blocksize = AES_BLOCK_SIZE;
@@ -356,7 +423,7 @@ QCryptoCipher *qcrypto_cipher_new(QCryptoCipherAlgorithm alg,
     cipher->alg = alg;
     cipher->mode = mode;
 
-    if (!qcrypto_cipher_validate_key_length(alg, nkey, errp)) {
+    if (!qcrypto_cipher_validate_key_length(alg, mode, nkey, errp)) {
         goto error;
     }