I have been studying Curve25519 and signal protocol since few days . What i came to know that in general Curve25519 uses "9" as base point but in signal base point used is convert_mont(9). convert_mont(9) is the function which generate a twisted edward curve key pair using montgomery private key as the parameter. Why is that?
Also it has been mentioned that in the docs that
XEd25519 signatures are valid Ed25519 signatures [1] and vice versa, provided the public keys are converted with the birational map.
which i think means that if Ed25519 signatures are calculated using convert_mont() then it is equivelent to the XEd25519 signature .
If i have to implement convert_mont() then how do i do airthmetic operation on in libsodium since i am pretty new to cryptography.
Thanks.