crypto: cts - don't support empty messages (c31a8719) · Commits · 戴 / test

My patches to make testmgr fuzz algorithms against their generic implementation detected that the arm64 implementations of "cts(cbc(aes))" handle empty messages differently from the cts template. Namely, the arm64 implementations forbids (with -EINVAL) all messages shorter than the block size, including the empty message; but the cts template permits empty messages as a special case. No user should be CTS-encrypting/decrypting empty messages, but we need to keep the behavior consistent. Unfortunately, as noted in the source of OpenSSL's CTS implementation [1], there's no common specification for CTS. This makes it somewhat debatable what the behavior should be. However, all CTS specifications seem to agree that messages shorter than the block size are not allowed, and OpenSSL follows this in both CTS conventions it implements. It would also simplify the user-visible semantics to have empty messages no longer be a special case. Therefore, make the cts template return -EINVAL on *all* messages shorter than the block size, including the empty message. [1] https://github.com/openssl/openssl/blob/master/crypto/modes/cts128.c Signed-off-by:

Eric Biggers <ebiggers@google.com> Signed-off-by:

Herbert Xu <herbert@gondor.apana.org.au>

crypto/cts.c

+11 −7

Original line number	Diff line number	Diff line
		@@ -152,12 +152,14 @@ static int crypto_cts_encrypt(struct skcipher_request *req)
		struct skcipher_request *subreq = &rctx->subreq;
		int bsize = crypto_skcipher_blocksize(tfm);
		unsigned int nbytes = req->cryptlen;
		int cbc_blocks = (nbytes + bsize - 1) / bsize - 1;
		unsigned int offset;

		skcipher_request_set_tfm(subreq, ctx->child);

		if (cbc_blocks <= 0) {
		if (nbytes < bsize)
		return -EINVAL;

		if (nbytes == bsize) {
		skcipher_request_set_callback(subreq, req->base.flags,
		req->base.complete,
		req->base.data);
		@@ -166,7 +168,7 @@ static int crypto_cts_encrypt(struct skcipher_request *req)
		return crypto_skcipher_encrypt(subreq);
		}

		offset = cbc_blocks * bsize;
		offset = rounddown(nbytes - 1, bsize);
		rctx->offset = offset;

		skcipher_request_set_callback(subreq, req->base.flags,
		@@ -244,13 +246,15 @@ static int crypto_cts_decrypt(struct skcipher_request *req)
		struct skcipher_request *subreq = &rctx->subreq;
		int bsize = crypto_skcipher_blocksize(tfm);
		unsigned int nbytes = req->cryptlen;
		int cbc_blocks = (nbytes + bsize - 1) / bsize - 1;
		unsigned int offset;
		u8 *space;

		skcipher_request_set_tfm(subreq, ctx->child);

		if (cbc_blocks <= 0) {
		if (nbytes < bsize)
		return -EINVAL;

		if (nbytes == bsize) {
		skcipher_request_set_callback(subreq, req->base.flags,
		req->base.complete,
		req->base.data);
		@@ -264,10 +268,10 @@ static int crypto_cts_decrypt(struct skcipher_request *req)

		space = crypto_cts_reqctx_space(req);

		offset = cbc_blocks * bsize;
		offset = rounddown(nbytes - 1, bsize);
		rctx->offset = offset;

		if (cbc_blocks <= 1)
		if (offset <= bsize)
		memcpy(space, req->iv, bsize);
		else
		scatterwalk_map_and_copy(space, req->src, offset - 2 * bsize,

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