Hash Generator

"The Get-FileHash cmdlet computes the hash value for a file by using a specified hash algorithm. A hash value is a unique value that corresponds to the content of the file. Rather than identifying the contents of a file by its file name, extension, or other designation, a hash assigns a unique value to the contents of a file. File names and extensions can be changed without altering the content of the file, and without changing the hash value. Similarly, the file's content can be changed without changing the name or extension. However, changing even a single character in the contents of a file changes the hash value of the file.

The purpose of hash values is to provide a cryptographically-secure way to verify that the contents of a file have not been changed. While some hash algorithms, including MD5 and SHA1, are no longer considered secure against attack, the goal of a secure hash algorithm is to render it impossible to change the contents of a file -- either by accident, or by malicious or unauthorized attempt -- and maintain the same hash value. You can also use hash values to determine if two different files have exactly the same content. If the hash values of two files are identical, the contents of the files are also identical."

Get-FileHash | microsoft.powershell.utility

I decided to use the Get-FileHash cmdlet as creating the generator with the cmdlet was slightly faster than using the HashAlgorithm class:

# Measured using System.Diagnostics.Stopwatch
0.1626268 seconds # Get-FileHash
0.2177895 seconds # HashAlgorithm Class

Get-FileHash -Algorithm accepts:

• MD5 (128 Bits)
• SHA1 (160 Bits)
• SHA256 (256 Bits)
• SHA384 (384 Bits)
• SHA512 (512 Bits)

Preview using sleep & seconds = 3:

nvhg.mp4

The computed hash depends on the file content, e.g. empty files have the same hash (which means that every change affects the hash - Avalanche effect):

# Scenario 1 (no content)
PS C:\Users\Nohuxi> Get-Content -LiteralPath 'C:\Users\Nohuxi\Desktop\Noverse0.txt' -Raw
PS C:\Users\Nohuxi> # No output, since empty

PS C:\Users\Nohuxi> 'MD5','SHA1','SHA256','SHA384','SHA512' | % { '{0}: {1}' -f $_,(Get-FileHash -LiteralPath 'C:\Users\Nohuxi\Desktop\Noverse0.txt' -Algorithm $_).Hash }
MD5: D41D8CD98F00B204E9800998ECF8427E
SHA1: DA39A3EE5E6B4B0D3255BFEF95601890AFD80709
SHA256: E3B0C44298FC1C149AFBF4C8996FB92427AE41E4649B934CA495991B7852B855
SHA384: 38B060A751AC96384CD9327EB1B1E36A21FDB71114BE07434C0CC7BF63F6E1DA274EDEBFE76F65FBD51AD2F14898B95B
SHA512: CF83E1357EEFB8BDF1542850D66D8007D620E4050B5715DC83F4A921D36CE9CE47D0D13C5D85F2B0FF8318D2877EEC2F63B931BD47417A81A538327AF927DA3E

# Scenario 2 (added content)
PS C:\Users\Nohuxi> Get-Content -LiteralPath 'C:\Users\Nohuxi\Desktop\Noverse1.txt' -Raw
1 # Content
PS C:\Users\Nohuxi>

PS C:\Users\Nohuxi> 'MD5','SHA1','SHA256','SHA384','SHA512' | % { '{0}: {1}' -f $_,(Get-FileHash -LiteralPath 'C:\Users\Nohuxi\Desktop\Noverse1.txt' -Algorithm $_).Hash }
MD5: C4CA4238A0B923820DCC509A6F75849B
SHA1: 356A192B7913B04C54574D18C28D46E6395428AB
SHA256: 6B86B273FF34FCE19D6B804EFF5A3F5747ADA4EAA22F1D49C01E52DDB7875B4B
SHA384: 47F05D367B0C32E438FB63E6CF4A5F35C2AA2F90DC7543F8A41A0F95CE8A40A313AB5CF36134A2068C4C969CB50DB776
SHA512: 4DFF4EA340F0A823F15D3F4F01AB62EAE0E5DA579CCB851F8DB9DFE84C58B2B37B89903A740E1EE172DA793A6E79D560E5F7F9BD058A12A280433ED6FA46510A

As you can see, adding a 1 to the file content has completely changed the hash values. You can try this yourself by editing the paths.

MD5("") 
0x d41d8cd98f00b204e9800998ecf8427e
SHA1("")
0x da39a3ee5e6b4b0d3255bfef95601890afd80709
SHA256("")
0x e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
SHA384("")
0x 38b060a751ac96384cd9327eb1b1e36a21fdb71114be07434c0cc7bf63f6e1da274edebfe76f65fbd51ad2f14898b95b
SHA512("")
0x cf83e1357eefb8bdf1542850d66d8007d620e4050b5715dc83f4a921d36ce9ce47d0d13c5d85f2b0ff8318d2877eec2f63b931bd47417a81a538327af927da3e

SHA-2 | wikipedia
MD5 | wikipedia
SHA-1 | wikipedia

Installation

Add-CM.ps1 will add a Generate Hash option to the context menu of any file/folder (if selecting a folder all files within the folder will get used):

Note

HashGen.ps1 has to be in your Downloads folder

There're 2 valid params which you can set (Add-CM.ps1 will ask for them):

• sleep (disabled by default means not present, as it is a switch)
  • If Y the file won't close instantly and waits for a specific time till it closes (seconds)
• seconds (default of 3)
  • Only has a impact, if sleep is enabled

Uninstallation

Remove the content menu entry and HashGen with:

Remove-Item -Path "HKCU:\Software\Classes\*\shell\NV-Hash" -Recurse -Force
Remove-Item -Path "HKCU:\Software\Classes\Directory\shell\NV-Hash" -Recurse -Force
Remove-Item -Path "$env:localappdata\Noverse\HashGen.ps1" -Force