How to Determine Digest Algorithm

[Patrick Brunschwig]

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I'm trying to find a good way to determine the digest algorithm that
GnuPG uses for a signed message. My problem is this: for PGP/MIME signed
messages, I need to know the algorithm before the message is created.
Therefore I create a signed dummy message, and extract from it the hash
algorithm. However, the problem is that this requires the user to type
the passphrase twice, which I would like to avoid.

Is there a better way to determine the hash algorithm without actually
creating a signed message?

Thanks,
Patrick
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