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, 73 insertions, 6 deletions

diff --git a/crypto/cipher-nettle.c b/crypto/cipher-nettle.c
index ed08782c35..3c982e483a 100644
--- a/crypto/cipher-nettle.c
+++ b/crypto/cipher-nettle.c
@@ -19,6 +19,8 @@
  */
 
 #include "qemu/osdep.h"
+#include "crypto/xts.h"
+
 #include <nettle/nettle-types.h>
 #include <nettle/aes.h>
 #include <nettle/des.h>
@@ -111,9 +113,14 @@ static void twofish_decrypt_wrapper(cipher_ctx_t ctx, cipher_length_t length,
 
 typedef struct QCryptoCipherNettle QCryptoCipherNettle;
 struct QCryptoCipherNettle {
+    /* Primary cipher context for all modes */
     void *ctx;
+    /* Second cipher context for XTS mode only */
+    void *ctx_tweak;
+    /* Cipher callbacks for both contexts */
     nettle_cipher_func *alg_encrypt;
     nettle_cipher_func *alg_decrypt;
+
     uint8_t *iv;
     size_t blocksize;
 };
@@ -151,13 +158,14 @@ QCryptoCipher *qcrypto_cipher_new(QCryptoCipherAlgorithm alg,
     switch (mode) {
     case QCRYPTO_CIPHER_MODE_ECB:
     case QCRYPTO_CIPHER_MODE_CBC:
+    case QCRYPTO_CIPHER_MODE_XTS:
         break;
     default:
         error_setg(errp, "Unsupported cipher mode %d", mode);
         return NULL;
     }
 
-    if (!qcrypto_cipher_validate_key_length(alg, nkey, errp)) {
+    if (!qcrypto_cipher_validate_key_length(alg, mode, nkey, errp)) {
         return NULL;
     }
 
@@ -185,8 +193,25 @@ QCryptoCipher *qcrypto_cipher_new(QCryptoCipherAlgorithm alg,
     case QCRYPTO_CIPHER_ALG_AES_256:
         ctx->ctx = g_new0(QCryptoNettleAES, 1);
 
-        aes_set_encrypt_key(&((QCryptoNettleAES *)ctx->ctx)->enc, nkey, key);
-        aes_set_decrypt_key(&((QCryptoNettleAES *)ctx->ctx)->dec, nkey, key);
+        if (mode == QCRYPTO_CIPHER_MODE_XTS) {
+            ctx->ctx_tweak = g_new0(QCryptoNettleAES, 1);
+
+            nkey /= 2;
+            aes_set_encrypt_key(&((QCryptoNettleAES *)ctx->ctx)->enc,
+                                nkey, key);
+            aes_set_decrypt_key(&((QCryptoNettleAES *)ctx->ctx)->dec,
+                                nkey, key);
+
+            aes_set_encrypt_key(&((QCryptoNettleAES *)ctx->ctx_tweak)->enc,
+                                nkey, key + nkey);
+            aes_set_decrypt_key(&((QCryptoNettleAES *)ctx->ctx_tweak)->dec,
+                                nkey, key + nkey);
+        } else {
+            aes_set_encrypt_key(&((QCryptoNettleAES *)ctx->ctx)->enc,
+                                nkey, key);
+            aes_set_decrypt_key(&((QCryptoNettleAES *)ctx->ctx)->dec,
+                                nkey, key);
+        }
 
         ctx->alg_encrypt = aes_encrypt_wrapper;
         ctx->alg_decrypt = aes_decrypt_wrapper;
@@ -197,7 +222,15 @@ QCryptoCipher *qcrypto_cipher_new(QCryptoCipherAlgorithm alg,
     case QCRYPTO_CIPHER_ALG_CAST5_128:
         ctx->ctx = g_new0(struct cast128_ctx, 1);
 
-        cast5_set_key(ctx->ctx, nkey, key);
+        if (mode == QCRYPTO_CIPHER_MODE_XTS) {
+            ctx->ctx_tweak = g_new0(struct cast128_ctx, 1);
+
+            nkey /= 2;
+            cast5_set_key(ctx->ctx, nkey, key);
+            cast5_set_key(ctx->ctx_tweak, nkey, key + nkey);
+        } else {
+            cast5_set_key(ctx->ctx, nkey, key);
+        }
 
         ctx->alg_encrypt = cast128_encrypt_wrapper;
         ctx->alg_decrypt = cast128_decrypt_wrapper;
@@ -210,7 +243,15 @@ QCryptoCipher *qcrypto_cipher_new(QCryptoCipherAlgorithm alg,
     case QCRYPTO_CIPHER_ALG_SERPENT_256:
         ctx->ctx = g_new0(struct serpent_ctx, 1);
 
-        serpent_set_key(ctx->ctx, nkey, key);
+        if (mode == QCRYPTO_CIPHER_MODE_XTS) {
+            ctx->ctx_tweak = g_new0(struct serpent_ctx, 1);
+
+            nkey /= 2;
+            serpent_set_key(ctx->ctx, nkey, key);
+            serpent_set_key(ctx->ctx_tweak, nkey, key + nkey);
+        } else {
+            serpent_set_key(ctx->ctx, nkey, key);
+        }
 
         ctx->alg_encrypt = serpent_encrypt_wrapper;
         ctx->alg_decrypt = serpent_decrypt_wrapper;
@@ -223,7 +264,15 @@ QCryptoCipher *qcrypto_cipher_new(QCryptoCipherAlgorithm alg,
     case QCRYPTO_CIPHER_ALG_TWOFISH_256:
         ctx->ctx = g_new0(struct twofish_ctx, 1);
 
-        twofish_set_key(ctx->ctx, nkey, key);
+        if (mode == QCRYPTO_CIPHER_MODE_XTS) {
+            ctx->ctx_tweak = g_new0(struct twofish_ctx, 1);
+
+            nkey /= 2;
+            twofish_set_key(ctx->ctx, nkey, key);
+            twofish_set_key(ctx->ctx_tweak, nkey, key + nkey);
+        } else {
+            twofish_set_key(ctx->ctx, nkey, key);
+        }
 
         ctx->alg_encrypt = twofish_encrypt_wrapper;
         ctx->alg_decrypt = twofish_decrypt_wrapper;
@@ -259,6 +308,7 @@ void qcrypto_cipher_free(QCryptoCipher *cipher)
     ctx = cipher->opaque;
     g_free(ctx->iv);
     g_free(ctx->ctx);
+    g_free(ctx->ctx_tweak);
     g_free(ctx);
     g_free(cipher);
 }
@@ -289,6 +339,12 @@ int qcrypto_cipher_encrypt(QCryptoCipher *cipher,
                     len, out, in);
         break;
 
+    case QCRYPTO_CIPHER_MODE_XTS:
+        xts_encrypt(ctx->ctx, ctx->ctx_tweak,
+                    ctx->alg_encrypt, ctx->alg_encrypt,
+                    ctx->iv, len, out, in);
+        break;
+
     default:
         error_setg(errp, "Unsupported cipher algorithm %d",
                    cipher->alg);
@@ -323,6 +379,17 @@ int qcrypto_cipher_decrypt(QCryptoCipher *cipher,
                     len, out, in);
         break;
 
+    case QCRYPTO_CIPHER_MODE_XTS:
+        if (ctx->blocksize != XTS_BLOCK_SIZE) {
+            error_setg(errp, "Block size must be %d not %zu",
+                       XTS_BLOCK_SIZE, ctx->blocksize);
+            return -1;
+        }
+        xts_decrypt(ctx->ctx, ctx->ctx_tweak,
+                    ctx->alg_encrypt, ctx->alg_decrypt,
+                    ctx->iv, len, out, in);
+        break;
+
     default:
         error_setg(errp, "Unsupported cipher algorithm %d",
                    cipher->alg);