I am using HMAC (hmac-sha256 to be precise) message authentication without encryption. My question is, is having a short message make it easy to determine what my secret key is?
My C# code is as follows
HMACSHA256 hmacSha256 = new HMACSHA256(new byte[]{0xfa, 0x35, 0x24, ..., 0x5e}); // 64 byte secret key
byte[] authForMessageA = hmacSha256.ComputeHash(new byte[]{0x25}); // very short message
byte[] authForMessageB = hmacSha256.ComputeHash(new byte[]{0x66}); // another message, same key
I am exposing both the message (0x25 and 0x66) along with their authentication hashes to the public, does this make it simple for a hacker to determine my secret key (brute force or otherwise)?