Implement AES-XTS mode
XTS mode is fully known as "xor-encrypt-xor with ciphertext-stealing".
This is the generalization of the XEX mode.
This implementation is limited to an 8-bits (1 byte) boundary, which
doesn't seem to be what was thought considering some test vectors [1].
This commit comes with tests, extracted from [1], and benchmarks.
Although, benchmarks aren't really nice here, as they work with a buffer
of a multiple of 16 bytes, which isn't a challenge for XTS compared to
XEX.
[1] http://csrc.nist.gov/groups/STM/cavp/documents/aes/XTSTestVectors.zip
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index 09379a0..3a7c159 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -509,6 +509,14 @@
#define MBEDTLS_CIPHER_MODE_XEX
/**
+ * \def MBEDTLS_CIPHER_MODE_XTS
+ *
+ * Enable Xor-encrypt-xor with ciphertext stealing mode (XTS) for symmetric
+ * ciphers.
+ */
+#define MBEDTLS_CIPHER_MODE_XTS
+
+/**
* \def MBEDTLS_CIPHER_MODE_OFB
*
* Enable Output Feedback mode (OFB) for symmetric ciphers.