[erlang-questions] Old and new crypto: sign, rsa_sign, verify, rsa_verify compatibility

John Doe <>
Thu Oct 24 01:07:51 CEST 2013


Hi,

Is it possible to make RSA signatures compatible between old and new crypto
methods? I can't find a way how to do this.
Here's an example, run in R16B02:

crypto:start().

%% these two keys are valid RSA keypair
PrivateKey =
[<<0,0,0,2,2,1>>,<<0,0,0,65,0,194,170,51,214,70,17,25,24,39,11,190,238,251,171,164,221,80,251,171,85,16,134,227,199,246,113,207,194,211,53,68,253,54,195,192,2,93,91,107,118,147,218,227,151,148,3,165,184,26,199,213,68,18,25,35,249,207,196,111,26,201,150,255,69>>,<<0,0,0,64,104,90,61,184,186,69,12,116,62,217,98,92,46,21,166,57,194,30,29,119,116,166,32,71,194,252,162,197,193,144,84,98,223,170,137,84,25,86,2,237,128,201,216,139,98,173,122,229,3,62,100,69,241,18,186,249,170,25,156,172,32,228,180,129>>].
PublicKey =
[<<0,0,0,2,2,1>>,<<0,0,0,65,0,194,170,51,214,70,17,25,24,39,11,190,238,251,171,164,221,80,251,171,85,16,134,227,199,246,113,207,194,211,53,68,253,54,195,192,2,93,91,107,118,147,218,227,151,148,3,165,184,26,199,213,68,18,25,35,249,207,196,111,26,201,150,255,69>>].

SizedBinary = fun(Binary) -> <<(size(Binary)):32/integer,  Binary/binary>>
end.

Payload = <<"Launch the nukes.">>.

Hash =  crypto:sha(Payload).

%%signed with old method
Signature = crypto:rsa_sign(SizedBinary(Hash), PrivateKey).

%%verify with old method - returns true
crypto:rsa_verify(SizedBinary(Hash), SizedBinary(Signature), PublicKey).

%%new method - returns false
crypto:verify(rsa, sha, {digest, Hash}, Signature, PublicKey).

%%another try of new method - throws an 'bad argument' exception
crypto:verify(rsa, sha, {digest, SizedBinary(Hash)},
SizedBinary(Signature), PublicKey).

%%new method yet again - returns false
crypto:verify(rsa, sha, {digest, Hash}, SizedBinary(Signature), PublicKey).
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