I'm implementing an `Basic Auth.` with User Hashed...

# ktor

[frank]

I'm implementing an Basic Auth. with User Hashed and I was checking the validation function for check if it's timing-attack safe.

I saw, that uses the equals(byte [] a, byte [] a2) method to validate credentials. So I think it would be timing-attack vulnerable.
Validate function:

public fun authenticate(credential: UserPasswordCredential): UserIdPrincipal? {
        val userPasswordHash = table[credential.name]
        if (userPasswordHash != null && digester(credential.password) contentEquals userPasswordHash) {
            return UserIdPrincipal(credential.name)
        }

        return null
}

Any alternative in Ktor lib or I'm wrong?

[Arjan van Wieringen]

Why would this be vulnerable to a timing attack?

[chiroptical]

If the user password hash is null you don’t digest. Is the digester constant time? You could always digest and then do the check?

[chiroptical]

(fwiw, I am not an expert here and would be curious about what others say)

[chiroptical]

Ohh, I might be conflating timing attacks. I think your question might be: is contentEquals constant time?

[frank]

@chiroptical Yes, I have doubts with contentEquals if is constant-time.

Looking the code, I would say that in the first if is time-attack vulnerable. I'm wrong?

@IntrinsicCandidate
public static boolean equals(byte[] a, byte[] a2) {
        if (a==a2)
            return true;
        if (a==null || a2==null)
            return false;

        int length = a.length;
        if (a2.length != length)
            return false;

        return ArraysSupport.mismatch(a, a2, length) < 0;
 }

[Arjan van Wieringen]

You might actually be right. A similar JVM (Scala) vulnerability: https://vulners.com/veracode/VERACODE:5933