Allow AES XTS decryption using duplicate keys.

This feature is enabled by default outside of FIPS builds
which ban such actions completely.

Encryption is always disallowed and will generate an error.
Reviewed-by: NTomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/9112)

crypto/evp/e_aes.c

@@ -63,6 +63,12 @@ typedef struct {
                     const unsigned char iv[16]);
 } EVP_AES_XTS_CTX;
 
+#ifdef FIPS_MODE
+static const int allow_insecure_decrypt = 0;
+#else
+static const int allow_insecure_decrypt = 1;
+#endif
+
 typedef struct {
     union {
         OSSL_UNION_ALIGN;
@@ -387,6 +393,7 @@ static int aesni_xts_init_key(EVP_CIPHER_CTX *ctx, const unsigned char *key,
                               const unsigned char *iv, int enc)
 {
     EVP_AES_XTS_CTX *xctx = EVP_C_DATA(EVP_AES_XTS_CTX,ctx);
+
     if (!iv && !key)
         return 1;
 
@@ -401,7 +408,8 @@ static int aesni_xts_init_key(EVP_CIPHER_CTX *ctx, const unsigned char *key,
          * This addresses Rogaway's vulnerability.
          * See comment in aes_xts_init_key() below.
          */
-        if (memcmp(key, key + bytes, bytes) == 0) {
+        if ((!allow_insecure_decrypt || enc)
+                && CRYPTO_memcmp(key, key + bytes, bytes) == 0) {
             EVPerr(EVP_F_AESNI_XTS_INIT_KEY, EVP_R_XTS_DUPLICATED_KEYS);
             return 0;
         }
@@ -804,6 +812,7 @@ static int aes_t4_xts_init_key(EVP_CIPHER_CTX *ctx, const unsigned char *key,
                                const unsigned char *iv, int enc)
 {
     EVP_AES_XTS_CTX *xctx = EVP_C_DATA(EVP_AES_XTS_CTX,ctx);
+
     if (!iv && !key)
         return 1;
 
@@ -818,7 +827,8 @@ static int aes_t4_xts_init_key(EVP_CIPHER_CTX *ctx, const unsigned char *key,
          * This addresses Rogaway's vulnerability.
          * See comment in aes_xts_init_key() below.
          */
-        if (memcmp(key, key + bytes, bytes) == 0) {
+        if ((!allow_insecure_decrypt || enc)
+                && CRYPTO_memcmp(key, key + bytes, bytes) == 0) {
             EVPerr(EVP_F_AES_T4_XTS_INIT_KEY, EVP_R_XTS_DUPLICATED_KEYS);
             return 0;
         }
@@ -3408,10 +3418,12 @@ BLOCK_CIPHER_custom(NID_aes, 128, 1, 12, gcm, GCM,
 
 static int aes_xts_ctrl(EVP_CIPHER_CTX *c, int type, int arg, void *ptr)
 {
-    EVP_AES_XTS_CTX *xctx = EVP_C_DATA(EVP_AES_XTS_CTX,c);
+    EVP_AES_XTS_CTX *xctx = EVP_C_DATA(EVP_AES_XTS_CTX, c);
+
     if (type == EVP_CTRL_COPY) {
         EVP_CIPHER_CTX *out = ptr;
         EVP_AES_XTS_CTX *xctx_out = EVP_C_DATA(EVP_AES_XTS_CTX,out);
+
         if (xctx->xts.key1) {
             if (xctx->xts.key1 != &xctx->ks1)
                 return 0;
@@ -3435,6 +3447,7 @@ static int aes_xts_init_key(EVP_CIPHER_CTX *ctx, const unsigned char *key,
                             const unsigned char *iv, int enc)
 {
     EVP_AES_XTS_CTX *xctx = EVP_C_DATA(EVP_AES_XTS_CTX,ctx);
+
     if (!iv && !key)
         return 1;
 
@@ -3460,7 +3473,8 @@ static int aes_xts_init_key(EVP_CIPHER_CTX *ctx, const unsigned char *key,
              *       BEFORE using the keys in the XTS-AES algorithm to process
              *       data with them."
              */
-            if (memcmp(key, key + bytes, bytes) == 0) {
+            if ((!allow_insecure_decrypt || enc)
+                    && CRYPTO_memcmp(key, key + bytes, bytes) == 0) {
                 EVPerr(EVP_F_AES_XTS_INIT_KEY, EVP_R_XTS_DUPLICATED_KEYS);
                 return 0;
             }

test/recipes/30-test_evp_data/evpciph.txt

@@ -1190,13 +1190,34 @@ Result = CIPHERFINAL_ERROR
 
 Title = AES XTS test vectors from IEEE Std 1619-2007
 
+# Using the same key twice for encryption is always banned.
 Cipher = aes-128-xts
+Operation = ENCRYPT
 Key = 0000000000000000000000000000000000000000000000000000000000000000
 IV = 00000000000000000000000000000000
 Plaintext = 0000000000000000000000000000000000000000000000000000000000000000
 Ciphertext = 917cf69ebd68b2ec9b9fe9a3eadda692cd43d2f59598ed858c02c2652fbf922e
 Result = KEY_SET_ERROR
 
+# Using the same key twice for decryption is banned in FIPS mode.
+#Cipher = aes-128-xts
+#FIPS = YES
+#Operation = DECRYPT
+#Key = 0000000000000000000000000000000000000000000000000000000000000000
+#IV = 00000000000000000000000000000000
+#Plaintext = 0000000000000000000000000000000000000000000000000000000000000000
+#Ciphertext = 917cf69ebd68b2ec9b9fe9a3eadda692cd43d2f59598ed858c02c2652fbf922e
+#Result = KEY_SET_ERROR
+
+# Using the same key twice for decryption is allowed outside of FIPS mode.
+Cipher = aes-128-xts
+#FIPS = NO
+Operation = DECRYPT
+Key = 0000000000000000000000000000000000000000000000000000000000000000
+IV = 00000000000000000000000000000000
+Plaintext = 0000000000000000000000000000000000000000000000000000000000000000
+Ciphertext = 917cf69ebd68b2ec9b9fe9a3eadda692cd43d2f59598ed858c02c2652fbf922e
+
 Cipher = aes-128-xts
 Key = 1111111111111111111111111111111122222222222222222222222222222222
 IV = 33333333330000000000000000000000