crypto: hash - Add import/export interface

It is often useful to save the partial state of a hash function
so that it can be used as a base for two or more computations.

The most prominent example is HMAC where all hashes start from
a base determined by the key.  Having an import/export interface
means that we only have to compute that base once rather than
for each message.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/ahash.c

@@ -146,6 +146,20 @@ static int ahash_setkey(struct crypto_ahash *tfm, const u8 *key,
 	return ahash->setkey(tfm, key, keylen);
 }
 
+int crypto_ahash_import(struct ahash_request *req, const u8 *in)
+{
+	struct crypto_ahash *tfm = crypto_ahash_reqtfm(req);
+	struct ahash_alg *alg = crypto_ahash_alg(tfm);
+
+	memcpy(ahash_request_ctx(req), in, crypto_ahash_reqsize(tfm));
+
+	if (alg->reinit)
+		alg->reinit(req);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(crypto_ahash_import);
+
 static unsigned int crypto_ahash_ctxsize(struct crypto_alg *alg, u32 type,
 					u32 mask)
 {

crypto/shash.c

@@ -172,6 +172,20 @@ int crypto_shash_digest(struct shash_desc *desc, const u8 *data,
 }
 EXPORT_SYMBOL_GPL(crypto_shash_digest);
 
+int crypto_shash_import(struct shash_desc *desc, const u8 *in)
+{
+	struct crypto_shash *tfm = desc->tfm;
+	struct shash_alg *alg = crypto_shash_alg(tfm);
+
+	memcpy(shash_desc_ctx(desc), in, crypto_shash_descsize(tfm));
+
+	if (alg->reinit)
+		alg->reinit(desc);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(crypto_shash_import);
+
 static int shash_async_setkey(struct crypto_ahash *tfm, const u8 *key,
 			      unsigned int keylen)
 {

include/crypto/hash.h

@@ -24,6 +24,7 @@ struct shash_desc {
 
 struct shash_alg {
 	int (*init)(struct shash_desc *desc);
+	int (*reinit)(struct shash_desc *desc);
 	int (*update)(struct shash_desc *desc, const u8 *data,
 		      unsigned int len);
 	int (*final)(struct shash_desc *desc, u8 *out);
@@ -116,6 +117,11 @@ static inline unsigned int crypto_ahash_reqsize(struct crypto_ahash *tfm)
 	return crypto_ahash_crt(tfm)->reqsize;
 }
 
+static inline void *ahash_request_ctx(struct ahash_request *req)
+{
+	return req->__ctx;
+}
+
 static inline int crypto_ahash_setkey(struct crypto_ahash *tfm,
 				      const u8 *key, unsigned int keylen)
 {
@@ -130,6 +136,14 @@ static inline int crypto_ahash_digest(struct ahash_request *req)
 	return crt->digest(req);
 }
 
+static inline void crypto_ahash_export(struct ahash_request *req, u8 *out)
+{
+	memcpy(out, ahash_request_ctx(req),
+	       crypto_ahash_reqsize(crypto_ahash_reqtfm(req)));
+}
+
+int crypto_ahash_import(struct ahash_request *req, const u8 *in);
+
 static inline int crypto_ahash_init(struct ahash_request *req)
 {
 	struct ahash_tfm *crt = crypto_ahash_crt(crypto_ahash_reqtfm(req));
@@ -262,6 +276,13 @@ int crypto_shash_setkey(struct crypto_shash *tfm, const u8 *key,
 int crypto_shash_digest(struct shash_desc *desc, const u8 *data,
 			unsigned int len, u8 *out);
 
+static inline void crypto_shash_export(struct shash_desc *desc, u8 *out)
+{
+	memcpy(out, shash_desc_ctx(desc), crypto_shash_descsize(desc->tfm));
+}
+
+int crypto_shash_import(struct shash_desc *desc, const u8 *in);
+
 static inline int crypto_shash_init(struct shash_desc *desc)
 {
 	return crypto_shash_alg(desc->tfm)->init(desc);

include/crypto/internal/hash.h

@@ -66,11 +66,6 @@ static inline struct ahash_request *ahash_dequeue_request(
 	return ahash_request_cast(crypto_dequeue_request(queue));
 }
 
-static inline void *ahash_request_ctx(struct ahash_request *req)
-{
-	return req->__ctx;
-}
-
 static inline int ahash_tfm_in_queue(struct crypto_queue *queue,
 					  struct crypto_ahash *tfm)
 {

include/linux/crypto.h

@@ -221,6 +221,7 @@ struct ablkcipher_alg {
 
 struct ahash_alg {
 	int (*init)(struct ahash_request *req);
+	int (*reinit)(struct ahash_request *req);
 	int (*update)(struct ahash_request *req);
 	int (*final)(struct ahash_request *req);
 	int (*digest)(struct ahash_request *req);