lib: Add hmac helpers

These run hmac for given data with given parameters
and returns stack allocated buffer. They are helpful
when doing lots of HMACs, such as the AWS4 signing
protocol.

src/lib/hmac.c

@@ -10,6 +10,7 @@
 #include "lib.h"
 #include "hmac.h"
 #include "safe-memset.h"
+#include "buffer.h"
 
 void hmac_init(struct hmac_context *_ctx, const unsigned char *key,
 		size_t key_len, const struct hash_method *meth)
@@ -59,3 +60,36 @@ void hmac_final(struct hmac_context *_ctx, unsigned char *digest)
 	ctx->hash->loop(ctx->ctxo, digest, ctx->hash->digest_size);
 	ctx->hash->result(ctx->ctxo, digest);
 }
+
+buffer_t *t_hmac_data(const struct hash_method *meth,
+		      const unsigned char *key, size_t key_len,
+		      const void *data, size_t data_len)
+{
+	struct hmac_context ctx;
+	i_assert(meth != NULL);
+	i_assert(key != NULL && key_len > 0);
+	i_assert(data != NULL || data_len == 0);
+
+	buffer_t *res = buffer_create_dynamic(pool_datastack_create(), meth->digest_size);
+	hmac_init(&ctx, key, key_len, meth);
+	if (data_len > 0)
+		hmac_update(&ctx, data, data_len);
+	unsigned char *buf = buffer_get_space_unsafe(res, 0, meth->digest_size);
+	hmac_final(&ctx, buf);
+	return res;
+}
+
+buffer_t *t_hmac_buffer(const struct hash_method *meth,
+			const unsigned char *key, size_t key_len,
+			const buffer_t *data)
+{
+	return t_hmac_data(meth, key, key_len, data->data, data->used);
+}
+
+buffer_t *t_hmac_str(const struct hash_method *meth,
+		     const unsigned char *key, size_t key_len,
+		     const char *data)
+{
+	return t_hmac_data(meth, key, key_len, data, strlen(data));
+}
+

src/lib/hmac.h

@@ -32,4 +32,14 @@ hmac_update(struct hmac_context *_ctx, const void *data, size_t size)
 	ctx->hash->loop(ctx->ctx, data, size);
 }
 
+buffer_t *t_hmac_data(const struct hash_method *meth,
+		      const unsigned char *key, size_t key_len,
+		      const void *data, size_t data_len);
+buffer_t *t_hmac_buffer(const struct hash_method *meth,
+			const unsigned char *key, size_t key_len,
+			const buffer_t *data);
+buffer_t *t_hmac_str(const struct hash_method *meth,
+		     const unsigned char *key, size_t key_len,
+		     const char *data);
+
 #endif