PowerShell v2 port of the Get-FileHash function. This version of Get-Hash supports hashing files and strings.

Get-Hash.ps1

function Get-Hash
{
    <#
    .SYNOPSIS

    Get-Hash is a PowerShell Version 2 port of Get-FileHash that supports hashing files, as well as, strings.

    .PARAMETER InputObject

    This is the actual item used to calculate the hash. This value will support [Byte[]] or [System.IO.Stream] objects.

    .PARAMETER FilePath

    Specifies the path to a file to hash. Wildcard characters are permitted.

    .PARAMETER Text

    A string to calculate a cryptographic hash for.

    .PARAMETER Encoding

    Specified the character encoding to use for the string passed to the Text parameter. The default encoding type is Unicode. The acceptable values for this parameter are:

    - ASCII
    - BigEndianUnicode
    - Default
    - Unicode
    - UTF32
    - UTF7
    - UTF8

    .PARAMETER Algorithm

    Specifies the cryptographic hash function to use for computing the hash value of the contents of the specified file. A cryptographic hash function includes the property that it is not possible to find two distinct inputs that generate the same hash values. Hash functions are commonly used with digital signatures and for data integrity. The acceptable values for this parameter are:
    
    - SHA1
    - SHA256
    - SHA384
    - SHA512
    - MACTripleDES
    - MD5
    - RIPEMD160
    
    If no value is specified, or if the parameter is omitted, the default value is SHA256.
    For security reasons, MD5 and SHA1, which are no longer considered secure, should only be used for simple change validation, and should not be used to generate hash values for files that require protection from attack or tampering.

    .NOTES
    
    This function was adapted from https://p0w3rsh3ll.wordpress.com/2015/02/05/backporting-the-get-filehash-function/
    Author: Jared Atkinson (@jaredcatkinson)
    License: BSD 3-Clause
    Required Dependencies: None
    Optional Dependencies: None

    .EXAMPLE

    Get-Hash -Text 'This is a string'

    .EXAMPLE

    Get-Hash -FilePath C:\This\is\a\filepath.exe

    #>

    param
    (
        [Parameter(Mandatory = $true, ParameterSetName = 'Object')]
        $InputObject,

        [Parameter(Mandatory = $true, ParameterSetName = 'File')]
        [string]
        [ValidateNotNullOrEmpty()]
        $FilePath,

        [Parameter(Mandatory = $true, ParameterSetName = 'Text')]
        [string]
        [ValidateNotNullOrEmpty()]
        $Text,

        [Parameter(ParameterSetName = 'Text')]
        [string]
        [ValidateSet('ASCII', 'BigEndianUnicode', 'Default', 'Unicode', 'UTF32', 'UTF7', 'UTF8')]
        $Encoding = 'Unicode',

        [Parameter()]
        [string]
        [ValidateSet("MACTripleDES", "MD5", "RIPEMD160", "SHA1", "SHA256", "SHA384", "SHA512")]
        $Algorithm = "SHA256"
    )

    switch($PSCmdlet.ParameterSetName)
    {
        File
        {
            try
            {
                $FullPath = Resolve-Path -Path $FilePath -ErrorAction Stop
                $InputObject = [System.IO.File]::OpenRead($FilePath)
                Get-Hash -InputObject $InputObject -Algorithm $Algorithm
            }
            catch
            {
                $retVal = New-Object -TypeName psobject -Property @{
                    Algorithm = $Algorithm.ToUpperInvariant()
                    Hash = $null
                }
            }
        }
        Text
        {
            $InputObject = [System.Text.Encoding]::$Encoding.GetBytes($Text)
            Get-Hash -InputObject $InputObject -Algorithm $Algorithm
        }
        Object
        {
            if($InputObject.GetType() -eq [Byte[]] -or $InputObject.GetType().BaseType -eq [System.IO.Stream])
            {
                # Construct the strongly-typed crypto object
                $hasher = [System.Security.Cryptography.HashAlgorithm]::Create($Algorithm)

                # Compute file-hash using the crypto object
                [Byte[]] $computedHash = $Hasher.ComputeHash($InputObject)
                [string] $hash = [BitConverter]::ToString($computedHash) -replace '-',''

                $retVal = New-Object -TypeName psobject -Property @{
                    Algorithm = $Algorithm.ToUpperInvariant()
                    Hash = $hash
                }

                $retVal
            }
        }
    }
}