Re: OAEP vs. PSS in PKCS#1

"yawnmoth" <terra1024@xxxxxxxxx> wrote in message news:ae8d6793-9903-415e-8a09-60a5a4058472@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Why doesn't PKCS#1 just create signatures by encrypting the hash?

Because there are attacks against the direct encryption of the hash.

have the Probabilistic Signature Scheme when you could just use
Optimal Asymmetric Encryption Padding on the hash?

Its about the proof of security. The proof for OAEP doesn't apply to signatures, the proof for PSS applies directly to signatures. OAEP is probably safe for signatures with a few modifications, but the PSS proof is more convenient.

The only thing I
can figure is this: that OAEP could be used but because it has,
embedded within it, a hash of the message, it requires larger keys
than PSS requires.

Actually the key size makes no difference. The key sizes required for security are larger than the key sizes required for either OAEP or PSS.


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