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The callers of crypto_sig_sign() assume that the signature size is always equivalent to the key size. This happens to be true for RSA, which is currently the only algorithm implementing the ->sign() callback. But it is false e.g. for X9.62 encoded ECDSA signatures because they have variable length. Prepare for addition of a ->sign() callback to such algorithms by letting the callback return the signature size (or a negative integer on error). When testing the ->sign() callback in test_sig_one(), use crypto_sig_maxsize() instead of crypto_sig_keysize() to verify that the test vector's signature does not exceed an algorithm's maximum signature size. There has been a relatively recent effort to upstream ECDSA signature generation support which may benefit from this change: https://lore.kernel.org/linux-crypto/20220908200036.2034-1-ignat@cloudflare.com/ However the main motivation for this commit is to reduce the number of crypto_sig_keysize() callers: This function is about to be changed to return the size in bits instead of bytes and that will require amending most callers to divide the return value by 8. Signed-off-by: Lukas Wunner <lukas@wunner.de> Reviewed-by: Stefan Berger <stefanb@linux.ibm.com> Cc: Ignat Korchagin <ignat@cloudflare.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>