In cryptography, a "salt" is an extra piece of data which is included when hashing a password. This makes rainbow-table attacks more difficult. Using a cryptographic hash function without an unpredictable salt increases the likelihood that an attacker could successfully find the hash value in databases of precomputed hashes (called rainbow-tables).

This rule raises an issue when a hashing function which has been specifically designed for hashing passwords, such as PBKDF2, is used with a non-random, reused or too short salt value. It does not raise an issue on base hashing algorithms such as sha1 or md5 as they should not be used to hash passwords.

Recommended Secure Coding Practices

• Use hashing functions generating their own secure salt or generate a secure random value of at least 16 bytes.
• The salt should be unique by user password.

Noncompliant Code Example

val salt = "notrandom".toByteArray()

val cipherSpec = PBEParameterSpec(salt, 10000) // Noncompliant, predictable salt
val spec = PBEKeySpec(password, salt, 10000, 256) // Noncompliant, predictable salt

Compliant Solution

val random = SecureRandom()
val salt = ByteArray(16)
random.nextBytes(salt)

val cipherSpec = PBEParameterSpec(salt, 10000) // Compliant
val spec = PBEKeySpec(password, salt, 10000, 256) // Compliant

See

• OWASP Top 10 2021 Category A2 - Cryptographic Failures
• OWASP Top 10 2017 Category A3 - Sensitive Data Exposure
• MITRE, CWE-759 - Use of a One-Way Hash without a Salt
• MITRE, CWE-760 - Use of a One-Way Hash with a Predictable Salt
• SANS Top 25 - Porous Defenses