crypto: chacha20poly1305 - Skip encryption/decryption for 0-len

If the length of the plaintext is zero, there's no need to waste cycles
on encryption and decryption. Using the chacha20poly1305 construction
for zero-length plaintexts is a common way of using a shared encryption
key for AAD authentication.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/crypto/chacha20poly1305.c b/crypto/chacha20poly1305.c
index 99c3cce0129035b5c41e2e8b4ebdab5ecd9fde2e..7b6b935cef23e0d4abdb948af4dcf16995a42c64 100644 (file)
--- a/crypto/chacha20poly1305.c
+++ b/crypto/chacha20poly1305.c
@@ -130,6 +130,9 @@ static int chacha_decrypt(struct aead_request *req)
        struct scatterlist *src, *dst;
        int err;
 
+       if (rctx->cryptlen == 0)
+               goto skip;
+
        chacha_iv(creq->iv, req, 1);
 
        sg_init_table(rctx->src, 2);
@@ -150,6 +153,7 @@ static int chacha_decrypt(struct aead_request *req)
        if (err)
                return err;
 
+skip:
        return poly_verify_tag(req);
 }
 
@@ -415,6 +419,9 @@ static int chacha_encrypt(struct aead_request *req)
        struct scatterlist *src, *dst;
        int err;
 
+       if (req->cryptlen == 0)
+               goto skip;
+
        chacha_iv(creq->iv, req, 1);
 
        sg_init_table(rctx->src, 2);
@@ -435,6 +442,7 @@ static int chacha_encrypt(struct aead_request *req)
        if (err)
                return err;
 
+skip:
        return poly_genkey(req);
 }