Scan for using bytes.Equal() to compare HMACs

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Metadata

ID: go-security/hmac-bytes

Language: Go

Severity: Error

Category: Security

Description

This rule flags instances where bytes.Equal() is used to compare HMACs. HMACs, or Hash-based Message Authentication Codes, are a type of cryptographic signature that are used to ensure the integrity and authenticity of a message. They are particularly sensitive to timing attacks, where an attacker can gain information about the secret key based on the time it takes to compare HMACs.

The bytes.Equal() function in Go does not have constant time complexity, meaning that the time it takes to run can vary based on the input. This can leak information about the HMAC, making it susceptible to timing attacks.

To avoid this vulnerability, you should use the hmac.Equal() function instead. This function has constant time complexity, meaning that it takes the same amount of time to run regardless of the input. This protects your HMAC comparisons from timing attacks and ensures the security of your code. For example, replace bytes.Equal(H, message) with hmac.Equal(H, message).

Non-Compliant Code Examples

func main(message, key []byte) {
    MAC = hmac.New(sha256.New, key);
    H = MAC.Sum(nil);
    bytes.Equal(H, message);
    bytes.Equal(message, H);
}

Compliant Code Examples

func main(message, key []byte) {
    MAC = hmac.New(sha256.New, key);
    H = MAC.Sum(nil);
    hmac.Equal(H, message);
    hmac.Equal(message, H);
}