Cryptographic hash algorithms such as MD2, MD4, MD5, MD6, HAVAL-128, DSA (which uses SHA-1), RIPEMD, RIPEMD-128, RIPEMD-160and SHA-1 are no longer considered secure, because it is possible to have collisions (little computational effort is enough to find two or more different inputs that produce the same hash).

Message authentication code (MAC) algorithms such as HMAC-MD5 or HMAC-SHA1 use weak hash functions as building blocks. Although they are not all proven to be weak, they are considered legacy algorithms and should be avoided.

Ask Yourself Whether

The hashed value is used in a security context like:

There is a risk if you answered yes to any of those questions.

Recommended Secure Coding Practices

Safer alternatives, such as SHA-256, SHA-512, SHA-3 are recommended, and for password hashing, it’s even better to use algorithms that do not compute too "quickly", like bcrypt, scrypt, argon2 or pbkdf2 because it slows down brute force attacks.

Sensitive Code Example

Imports System.Security.Cryptography

Sub ComputeHash()

    ' Review all instantiations of classes that inherit from HashAlgorithm, for example:
    Dim hashAlgo As HashAlgorithm = HashAlgorithm.Create() ' Sensitive
    Dim hashAlgo2 As HashAlgorithm = HashAlgorithm.Create("SHA1") ' Sensitive
    Dim sha As SHA1 = New SHA1CryptoServiceProvider() ' Sensitive
    Dim md5 As MD5 = New MD5CryptoServiceProvider() ' Sensitive

    ' ...
End Sub

Class MyHashAlgorithm
    Inherits HashAlgorithm ' Sensitive

    ' ...
End Class

Compliant Solution

Imports System.Security.Cryptography

Sub ComputeHash()
    Dim sha256 = New SHA256CryptoServiceProvider() ' Compliant
    Dim sha384 = New SHA384CryptoServiceProvider() ' Compliant
    Dim sha512 = New SHA512CryptoServiceProvider() ' Compliant

    ' ...
End Sub

See