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 <ja...@zx2c4.com>
Cc: <sta...@vger.kernel.org>
---
crypto/chacha20poly1305.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/crypto/chacha20poly1305.c b/crypto/chacha20poly1305.c
index 99c3cce..7b6b935 100644
--- 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);
}
--
2.6.3
--
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