ECDSA Verify Signature in C# using public key and signature from Java

Question

I have a public key and signature generated in Java which I would like to verify in C# using ECDsaCng. The public key is MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAExeg15CVOUcspdO

Answer 1

The cause is a different format. Microsoft expects the format r|s while your signature is specified in the ASN.1-format (which is explained in the context of ECDSA here):

0x30|b1|0x02|b2|r|0x02|b3|s
b1 = Length of remaining data
b2 = Length of r
b3 = Length of s 

Your signature

30440220534465047322bbebe9db49e23e073fc9d71d2b6cdf0deab11b7c7055c168e1800220093bf123cc266534b412bca0629d51df4af4c49a8af475cdd85fb14f3279d80a

can be separated in the following portions

30 44 02 20 534465047322bbebe9db49e23e073fc9d71d2b6cdf0deab11b7c7055c168e180 02 20 093bf123cc266534b412bca0629d51df4af4c49a8af475cdd85fb14f3279d80a

so that the individual portions can be easily identified:

b1 = 0x44
b2 = 0x20
r  = 0x534465047322bbebe9db49e23e073fc9d71d2b6cdf0deab11b7c7055c168e180 
b3 = 0x20
s  = 0x093bf123cc266534b412bca0629d51df4af4c49a8af475cdd85fb14f3279d80a

Thus

r|s = 534465047322bbebe9db49e23e073fc9d71d2b6cdf0deab11b7c7055c168e180093bf123cc266534b412bca0629d51df4af4c49a8af475cdd85fb14f3279d80a

If you run your code using this format, verification is successful.