# code from http://aperturescience.su
Function Get-FileHash
{
<#
.SYNOPSIS
Gets a hash value for the file specified
 
.DESCRIPTION
With this function you can calculate the hash of the contents of a specified file. Hash algorithms supported include SHA1, SHA2 256/348/512, MD5 and RIPEMD160
 
.PARAMETER File
[PIPELINE] File to get hash of.
 
.PARAMETER HashAlgorith
[OPTIONAL] The hash algorithm to use, must be either sha1, sha256, sha384, sha512, md5 or ripemd160
 
.PARAMETER Group
[SWITCH] Group by bytes, by default no grouping and hash returned as single long string. If specified byptes separated by "-"
 
.INPUTS
Accepts strings of paths to files in Pipeline
 
.OUTPUTS
hash of file
 
.EXAMPLE
get-FileHash c:\myfile.txt
Get hash (SHA256) of file, c:\myfile.txt
 
.EXAMPLE
get-FileHash c:\myfile.txt -HashAlgorithm md5
Get md5 hash of file, c:\myfile.txt
 
.EXAMPLE
dir c:\afolder | foreach { $_.fullname} | get-FileHash
get (SHA256) hashes for all files in c:\afolder
 
.NOTES
NAME: Get-FileHash
LASTEDIT: 2012-11-15 11:15:00
KEYWORDS:
 
.LINK
https://blogs.technet.com/b/msrc/archive/2012/11/13/verifying-update-hashes.aspx?Redirected=true
 
.LINK
http://blogs.msdn.com/b/mwilbur/archive/2007/03/14/get-sha256.aspx
 
.LINK
http://aperturescience.su/
#>
[CMDLetBinding()]
param
(
  [Parameter(mandatory=$true, valuefrompipeline=$true)] [ValidateScript({Test-Path $_ -PathType 'lea'})] [String] $File,
  [ValidateSet("sha1", "sha256", "sha384", "sha512", "md5", "ripemd160")] $HashAlgorithm = "sha256",
  [switch] $Group
)
 
Process
{
        #variable to store hash of the file
        $hash
       
        #select the correct hash function
        switch ($HashAlgorithm)
        {
                "sha1"
                        {
                                $hash = [system.bitconverter]::tostring([System.Security.Cryptography.sha1]::create().computehash([system.io.file]::openread((resolve-path $file))))
                        }
                "sha256"
                        {
                                $hash = [system.bitconverter]::tostring([System.Security.Cryptography.sha256]::create().computehash([system.io.file]::openread((resolve-path $file))))
                        }              
                "sha384"
                        {
                                $hash = [system.bitconverter]::tostring([System.Security.Cryptography.sha384]::create().computehash([system.io.file]::openread((resolve-path $file))))
                        }              
                "sha512"
                        {
                                $hash = [system.bitconverter]::tostring([System.Security.Cryptography.sha512]::create().computehash([system.io.file]::openread((resolve-path $file))))
                        }              
                "md5"
                        {
                                $hash = [system.bitconverter]::tostring([System.Security.Cryptography.md5]::create().computehash([system.io.file]::openread((resolve-path $file))))
                        }
                "ripemd160"
                        {
                                $hash = [system.bitconverter]::tostring([System.Security.Cryptography.ripemd160]::create().computehash([system.io.file]::openread((resolve-path $file))))
                        }
        }
       
       
       
        #leave the default grouping of byte pairs?
        if ($Group)
        {
                return $hash
        }
        else
        {
                return ($hash -replace "-","")
        }
}
 
}
# code from http://aperturescience.su