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Michael S. Mimoso, Editorial Director
The following is an example, written in Visual Basic, of how to compute the SHA-256 hash for the data string "myPassword" and display it in a label called Label1:
Imports System.Text
Public Class Form1
End Function
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Imports System.Security.Cryptography
Private Function ComputeSHA256Hash(ByVal Password As String) As String
' Convert Password into a byte array.
Dim passwordBytes As Byte()
passwordBytes = Encoding.UTF8.GetBytes(Password)
' Initialize the SHA256 hashing algorithm class
Dim shaM As New SHA256Managed()
' Compute hash value of the password.
Dim hashBytes As Byte()
hashBytes = shaM.ComputeHash(passwordBytes)
' Convert hash into a base64-encoded string.
ComputeSHA256Hash = Convert.ToBase64String(hashBytes)
Label1.Text = ComputeSHA256Hash("myPassword")
End Sub
End Class
The ComputeSHA256Hash function uses the .NET Framework Class Library System.Security.Cryptography class. It takes the string Password and turns it into a byte-array. It then runs those bytes through the SHA256Managed computation function provided by the class and returns a 44-bit string of the hash that's created. It finally displays via Labe1.Text. The hash for myPassword using this program is dlSbgn7EbnBf0DgxgT+lIXIzjw38vXEe1EuBqW2sUcY=. If you change the input to mzPassword, so just one character different, the hash changes to something completely different - XkdNLN2VuBgcMjhI/Dg0ioj4Eds6FLDF3lRlBxt+I4U=.
For security reasons, if you are using hash values to store passwords, you may well want to use a salt, as this makes a hashed-password less immune to dictionary attacks. Not only would the hacker have to develop a hash for every commonly known password, but also for every commonly known password multiplied by the nearly infinite number of possible salts.
This was first published in July 2010
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