I imported the key into DeltaChat 1.49 and tried adding this contact to DeltaChat 2.35.
Failed to receive a message: Error in Secure-Join ‘vc-request’ message handling: failed sending auth-required handshake message: Failed to create send jobs: IO error: Hash digest size (Sha256) must at least match key size (P521(..)): Hash digest size (Sha256) must at least match key size (P521(..)). Please report this bug to delta@merlinux.eu or https://support.delta.chat/.
Delta Chat version 2.35
We never generated P-521 keys, their use is not tested and not supported. We use SHA-256 for signatures, but P-521 keys require using at least SHA-512.
Importing the keys is not supported, see FAQ entry and the answer at
I also don’t understand why you want to use NIST P-521 keys, NIST curves are harder to implement securely than Ed25519 and NIST P-521 is just slower than NIST P-256.
The rPGP documentation says p521 is supported.
Why can’t it be used in DeltaChat?
If something is supported in rPGP, it does not mean it is supported in Delta Chat. We only test Ed25519+Curve25519 v4 keys and RSA 2048 keys because this is what old versions of Delta Chat generated.
In this case it did not work because we used SHA-256 regardless of the key. It may or may not work after the change, but we don’t test with P-521 keys.
Importing the keys was specifically removed to avoid us debugging all kind of keys that users typically generate when presented with options to generate the key, like insecure DSA, slow P-521 and RSA-8192 (also supported in rPGP, but if you import it you are on your own) keys, nonstandard GnuPG keys etc.