Call MakeAssertionAsync() function and get error: " trailing garbage ".

[holiday1228]

Hi Sirs,

I implement a Web API services with version=2.0.2.0, but I meet a problem when I call MakeAssertionAsync() function in my code and always get error message " trailing garbage ".
I try to trace by myself and it seems with something wrong during verifying signature by public key.
I need some suggestions to resolve this problem for me, could you help?

The signature return from browser is
304402205cfa0302023a989a6f6d2a6693c2512bd7c2b99c45ab960f938d54670c24b95102200cdd2e17344814f3f4fecee3c3da1b7c42bcc1cf4cf7d40956e8df249c55e2a4

AuthenticatorData is
vBOPJxfou_mSSUwH_dHQftsCIU6COZhuxt6dw9e5PKgBAAAACA

ClientData is
eyJ0eXBlIjoid2ViYXV0aG4uZ2V0IiwiY2hhbGxlbmdlIjoiNUNqMjlid2tjOFhmckFSYVNabTVqUSIsIm9yaWdpbiI6Imh0dHBzOi8vcHR3ZG4wNC5wZWdhdHJvbmNvcnAuY29tOjQ0NDMiLCJjcm9zc09yaWdpbiI6ZmFsc2V9

Public key is
pQECAyYgASFYIBDiyG/IEegVjpEDRBFk/FlB1nQUalKXcnYL6U1DyoXuIlggYEZpTnxxF9AyAihWAvvv2GJbm3NW8/cu13+Eu1wKr5A=

[abergs]

I have not encountered this error myself, but it sounds like an encoding issue?
Found this while googling, seems to be a similar issue https://devblogs.microsoft.com/oldnewthing/20210923-00/?p=105723

[aseigler]

Data formats are all over the place, but the signature is good.

[Fact]
public void TestHoliday1228Data()
{
    byte[] clientData = Convert.FromBase64String("eyJ0eXBlIjoid2ViYXV0aG4uZ2V0IiwiY2hhbGxlbmdlIjoiNUNqMjlid2tjOFhmckFSYVNabTVqUSIsIm9yaWdpbiI6Imh0dHBzOi8vcHR3ZG4wNC5wZWdhdHJvbmNvcnAuY29tOjQ0NDMiLCJjcm9zc09yaWdpbiI6ZmFsc2V9");
    byte[] hashedClientDataJson = System.Security.Cryptography.SHA256.HashData(clientData);
    byte[] sig = Convert.FromHexString("304402205cfa0302023a989a6f6d2a6693c2512bd7c2b99c45ab960f938d54670c24b95102200cdd2e17344814f3f4fecee3c3da1b7c42bcc1cf4cf7d40956e8df249c55e2a4");
    byte[] ad = Base64Url.Decode("vBOPJxfou_mSSUwH_dHQftsCIU6COZhuxt6dw9e5PKgBAAAACA");
    byte[] cpkBytes = Convert.FromBase64String("pQECAyYgASFYIBDiyG/IEegVjpEDRBFk/FlB1nQUalKXcnYL6U1DyoXuIlggYEZpTnxxF9AyAihWAvvv2GJbm3NW8/cu13+Eu1wKr5A=");
    CredentialPublicKey cpk = new CredentialPublicKey(cpkBytes);
    byte[] data = DataHelper.Concat(ad, hashedClientDataJson);
    Assert.True(cpk.Verify(data, sig));
}
        

[holiday1228]

@abergs , @aseigler
Thanks for your help and info, I'll try it.
If I resolved, I'll feedback to you.

[holiday1228]

Update.
I've resolve this problem. Before doing verify, I convert the hex string to byte array which receive from client.
The test case make a grate help for me. Thanks your guys a lots.