The maximum message length for a signature scheme is related to the hash
function used, not the key size. But hash functions usually have a input
length limit >= 2^64 bits, more than enough for any message you might want
to sign.
The reason you're seeing "key too short" is that the key is too short to
sign any message in that signature scheme, because of the hash output size
and padding length.
----- Original Message -----
From: "Sergio Andrés" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Tuesday, November 29, 2005 2:41 AM
Subject: message length in RSA signature
Hi all,
I have a doubt about the maximum message length allowed to generate a RSA
signature.
The message length is 36 bytes, and I would like to know which is the
minimum size of N for this message.
In general, I would need the relation between message length and N size.
Although I have read that there is no limit on message length, I got an
execution error when the key is too short (size(N) = 45 bytes).
I use Crypto++ Version 4.1.
My code is the following:
// the private key is encoded Hexadecimal
StringSource sPri(p_priclave, true, new HexDecoder);
RSASSA_PKCS1v15_SHA_Signer privkey(sPri);
AutoSeededRandomPool rp;
std::string sSignature;
StringSource(p_msg, true, new SignerFilter(rp, privkey, new
StringSink(sSignature)));
I hope you can help me.
Thanks in advance.
Sergio.
