Generate secrets with cryptographically secure RNG!

import "math/rand"
func generateAES256Key() ([]byte, error) {
    var key = make([]byte, 32)
    if _, err := rand.Read(key); err != nil {
        return nil, err
    }
    return key, nil
}

When generating random values for cryptographic algorithms (keys, nonces etc.), always generate them with a cryptographically secure random number generator (CSPRNG). Usually math libraries (like Go’s math/rand) provide a RNG implementation that is optimized for performance rather than security. Thus, random numbers generated with these libraries are usually not suited for cryptographic operations. Instead always use RNGs which explicitly state that they implement a CSPRNG like Go’s crypto/rand module.