RFR: 8271566: DSA signature length value is not accurate in P11Signature

[Valerie Peng]

On Mon, 2 Aug 2021 19:31:54 GMT, Martin Balao <mbalao at openjdk.org> wrote:

> As described in JDK-8271566 [1], this patch proposal is intended to fix a problem that arises when using DSA keys that have a 256-bits (or larger) G parameter for signatures (either signing or verifying). There were some incorrect assumptions and hard-coded length values in the code before. Please note that, for example, the tuple (2048, 256) for DSA is valid according to FIPS PUB 186-4.
> 
> Beyond the specific issues in signatures, I decided to provide a broader solution and enable key parameter retrieval for other key types (EC, DH) when possible. This is, when the key is not sensitive. One thing that I should note here is that token keys (those that have the CKA_TOKEN attribute equal to 'true') are considered sensitive in this regard, at least by the NSS Software Token implementation. I don't have access to other vendor implementations but if there is any concern, we can adjust the constraint to NSS-only. However, I'm not sure which use-case would require to get private keys out of a real token, weakening its security. I'd be more conservative here and not query the values if not sure that it will succeed.
> 
> No regressions found in jdk/sun/security/pkcs11. A new test added: LargerDSAKey.
> 
> --
> [1] - https://bugs.openjdk.java.net/browse/JDK-8271566

src/jdk.crypto.cryptoki/share/classes/sun/security/pkcs11/P11Signature.java line 123:

> 121: 
> 122:     // signature length expected or 0 for unknown
> 123:     private int signatureLength;

nit: use a shorter name, e.g. sigLen, so to fit in one line.

src/jdk.crypto.cryptoki/share/classes/sun/security/pkcs11/P11Signature.java line 817:

> 815:     }
> 816: 
> 817:     private byte[] asn1ToDSA(byte[] sig) throws SignatureException {

Have you considered keeping this as a static method but add one more int argument, i.e. signature length? It seems that the method asn1ToECDSA() can be made static too.

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PR: https://git.openjdk.java.net/jdk/pull/4961