# Need for "NoDigest" Signatures, other comments

Matthew Meyer (mmeyer@aurorasim.com)
Fri, 27 Aug 1999 11:15:45 -0400

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    Date: Fri, 27 Aug 1999 11:15:45 -0400

    From: mmeyer@aurorasim.com (Matthew Meyer)

    To: java-security@java.sun.com

    Subject: Need for "NoDigest"  Signatures, other comments

Java Security Team,

In general, I am pleased with the current JCA/JCE specification, and am
building my systems to these interfaces. One issue I encountered with
building on SSL implementation to these interfaces involves the manner
in which the SSL/TLS specification defines a digital signature with the
RSA algorithm. If the CertificateVerify message is sent from a client
for authentication, for example, than an RSA signature which involves a
concatenated hash of MD5 + SHA signatures of various handshake
quantities is used. A similar signature is used in the case that
temporary RSA keys are used for key exchange and the server must sign
the temporary keys with his long term signature keys. The current JCA
specification does not currently define such a signature. One solution
might be to define a "No Digest" signature which more less involves raw
encryption with the private key and the appropriate padding scheme. The
algorithm descriptor might be NoDigestwithRSA. The input then, would be
an arbitrary hash. Another solution would be for RSA-based JCE ciphers
to allow encryption operations with a private key. This needs to be
defined/required, however, and I don't believe the current providers
allow for this. Note that a "SSLSignature" which implements
Signature wouldn't work for the CertificateVerify message, because the
inputs to the two hashing algorithms are in fact different. There are
workarounds, such as making an RSAPrivateKey look like an RSAPublicKey,
and vice versa, but they only work for keys which live in software and
whose values can be queried.

Finally, I am not seeing the defined algorithm/padding names for RSA
encryption with the JCE, and looking at a few providers I am seeing in
fact some small differences in how they name their RSA. Am I missing
the appropriate document somewhere, or is this just a loose end that
needs to be cleaned up in JCE?.

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