Use of an inappropriate cryptographic hashing algorithm on passwords

Using a insufficiently computationally hard hash function can leave data vulnerable, and should not be used for password hashing.

A strong cryptographic hash function should be resistant to:

• Pre-image attacks. If you know a hash value h(x), you should not be able to easily find the input x.
• Collision attacks. If you know a hash value h(x), you should not be able to easily find a different input y with the same hash value h(x) = h(y).
• Brute force. If you know a hash value h(x), you should not be able to find an input y that computes to that hash value using brute force attacks without significant computational effort.
  All of MD5, SHA-1, SHA-2 and SHA-3 are weak against offline brute forcing, since they are not computationally hard. This includes SHA-224, SHA-256, SHA-384 and SHA-512, which are in the SHA-2 family.

Password hashing algorithms are designed to be slow and/or memory intenstive to compute, which makes brute force attacks more difficult.

Recommendation

Ensure that for password storage you should use a computationally hard cryptographic hash function, such as:

• Argon2
• scrypt
• bcrypt
• PBKDF2

Example

The following examples show a function that hashes a password using a cryptographic hashing algorithm. In the first case the SHA-512 hashing algorithm is used. It is vulnerable to offline brute force attacks:

let passwordData = Data(passwordString.utf8)
let passwordHash = Crypto.SHA512.hash(data: passwordData)

// ...

if Crypto.SHA512.hash(data: Data(passwordString.utf8)) == passwordHash {
    // ...
}

Here is the same function using Argon2, which is suitable for password hashing:

import Argon2Swift

let salt = Salt.newSalt()
let result = try! Argon2Swift.hashPasswordString(password: passwordString, salt: salt)
let passwordHash = result.encodedString()

// ...

if try! Argon2Swift.verifyHashString(password: passwordString, hash: passwordHash) {
    // ...
}

References

• OWASP: Password Storage Cheat Sheet
• libsodium: libsodium bindings for other languages
• GitHub: Argon2Swift
• Common Weakness Enumeration: CWE-327.
• Common Weakness Enumeration: CWE-328.
• Common Weakness Enumeration: CWE-916.