Hashing Files on the Windows Command Line

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Part of my modular PowerShell setup series and the ongoing saga of lost awesome software tools.

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🧰 The Setup

If you’ve ever right-clicked a file in Windows expecting a “Generate Hash” option only to find... nothing — you’re not alone. I used to have a perfect little portable tool with shell integration for hashing. But one day, it vanished from my C:\Portables directory. Instead of chasing it down, I found myself diving back into old-school command-line tools and realized a lot can still be done with built-ins like certutil.

This post is about:

• Wrapping a simple hashing utility in PowerShell

• Understanding how and why hashing works

• Kicking off a few side quests around crypto, profiles, and home-labbing

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⚙️ The Classic CMD One-liner

echo|set /p="foobar" > %TMP%\hash.txt | certutil -hashfile %TMP%\hash.txt SHA256 | findstr /v "hash"

This hashes the string foobar using SHA256 without appending a newline. That’s crucial. Using echo "foobar" would hash foobar\n, which is a different hash.

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🧪 Step-by-step (explained)

Supported algorithms:

• MD2, MD4, MD5

• SHA1, SHA256, SHA384, SHA512

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🧱 PowerShell Wrapper: Hash-String

Put this in ~\Documents\PowerShell\PSProfile.d\hash.ps1:

powershellCopyEditfunction Hash-String {
    param (
        [Parameter(Mandatory)]
        [string]$InputString,

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

    $tmpFile = [System.IO.Path]::GetTempFileName()
    [System.IO.File]::WriteAllText($tmpFile, $InputString)

    certutil -hashfile $tmpFile $Algorithm |
        Where-Object { $_ -notmatch "hash of|certutil" }

    Remove-Item $tmpFile
}

Usage:

powershellCopyEditHash-String -InputString "foobar" -Algorithm SHA256

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🧬 Why Hashes Matter

• ✅ Verify downloads with SHA256 hashes

• ✅ Secure passwords with irreversible hashing

• ✅ Digital signatures & TLS/SSL

• ✅ Git, blockchains, Merkle Trees... it's all hashes.

Hashes are the checksum of our digital lives.

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🗂 Modular Profiles with PSProfile.d

Like /etc/profile.d on Linux, I’m modularizing my Windows shell setup:

powershellCopyEdit# In $PROFILE
Get-ChildItem "$HOME\Documents\PowerShell\PSProfile.d" -Filter *.ps1 |
    ForEach-Object { . $_.FullName }

Drop your tools in PSProfile.d and you’ve got a portable, composable shell setup.

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🏗 Side Quest: Active Directory, Certs & More

Working with certutil reminded me I really should stand up a Windows Server 2019 VM inside my Proxmox cluster and finally add a domain controller to my home network.

Why?

• Local DNS, SSO, and central auth

• Experiment with GPOs and PKI

• Self-signed internal CA to play with smartcards or TLS

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🔮 Teaser: SHA-3 and the Weird Math

Everyone knows about MD5 and SHA-2. But SHA-3 (based on Keccak) is something else entirely — a "sponge function" that's mathematically quite different. I'm planning a whole future post on it once I get my head around the math and its growing role in post-quantum cryptography and hardware implementations.

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🧩 TL;DR

• Hash files or strings in Windows using certutil

• PowerShell makes it portable and repeatable

• Modular shell setups are 🔥

• Hashes underpin almost all of modern digital life

• And this is just the beginning...

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Got feedback? Need a GUI hash tool or want to explore digital signatures or SHA-3 next? Let me know. I’m building out a full FOSS-friendly workflow for Windows, Linux, and hybrid setups.