crypto: aes - create AES library based on the fixed time AES code

Take the existing small footprint and mostly time invariant C code
and turn it into a AES library that can be used for non-performance
critical, casual use of AES, and as a fallback for, e.g., SIMD code
that needs a secondary path that can be taken in contexts where the
SIMD unit is off limits (e.g., in hard interrupts taken from kernel
context)
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/Kconfig

@@ -1066,6 +1066,9 @@ config CRYPTO_GHASH_CLMUL_NI_INTEL
 
 comment "Ciphers"
 
+config CRYPTO_LIB_AES
+	tristate
+
 config CRYPTO_AES
 	tristate "AES cipher algorithms"
 	select CRYPTO_ALGAPI
@@ -1089,6 +1092,7 @@ config CRYPTO_AES
 config CRYPTO_AES_TI
 	tristate "Fixed time AES cipher"
 	select CRYPTO_ALGAPI
+	select CRYPTO_LIB_AES
 	help
 	  This is a generic implementation of AES that attempts to eliminate
 	  data dependent latencies as much as possible without affecting

include/crypto/aes.h

@@ -37,4 +37,38 @@ int crypto_aes_set_key(struct crypto_tfm *tfm, const u8 *in_key,
 		unsigned int key_len);
 int crypto_aes_expand_key(struct crypto_aes_ctx *ctx, const u8 *in_key,
 		unsigned int key_len);
+
+/**
+ * aes_expandkey - Expands the AES key as described in FIPS-197
+ * @ctx:	The location where the computed key will be stored.
+ * @in_key:	The supplied key.
+ * @key_len:	The length of the supplied key.
+ *
+ * Returns 0 on success. The function fails only if an invalid key size (or
+ * pointer) is supplied.
+ * The expanded key size is 240 bytes (max of 14 rounds with a unique 16 bytes
+ * key schedule plus a 16 bytes key which is used before the first round).
+ * The decryption key is prepared for the "Equivalent Inverse Cipher" as
+ * described in FIPS-197. The first slot (16 bytes) of each key (enc or dec) is
+ * for the initial combination, the second slot for the first round and so on.
+ */
+int aes_expandkey(struct crypto_aes_ctx *ctx, const u8 *in_key,
+		  unsigned int key_len);
+
+/**
+ * aes_encrypt - Encrypt a single AES block
+ * @ctx:	Context struct containing the key schedule
+ * @out:	Buffer to store the ciphertext
+ * @in:		Buffer containing the plaintext
+ */
+void aes_encrypt(const struct crypto_aes_ctx *ctx, u8 *out, const u8 *in);
+
+/**
+ * aes_decrypt - Decrypt a single AES block
+ * @ctx:	Context struct containing the key schedule
+ * @out:	Buffer to store the plaintext
+ * @in:		Buffer containing the ciphertext
+ */
+void aes_decrypt(const struct crypto_aes_ctx *ctx, u8 *out, const u8 *in);
+
 #endif

lib/crypto/Makefile

 # SPDX-License-Identifier: GPL-2.0
 
+obj-$(CONFIG_CRYPTO_LIB_AES) += libaes.o
+libaes-y := aes.o
+
 obj-$(CONFIG_CRYPTO_LIB_ARC4) += libarc4.o
 libarc4-y := arc4.o