# 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
    

---

### ⚙️ The Classic CMD One-liner

```plaintext
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.

---

### 🧪 Step-by-step (explained)

| Component | Explanation |
| --- | --- |
| `echo` | set /p="foobar"\` |
| `> %TMP%\hash.txt` | Writes the string to a temp file. |
| `certutil -hashfile file SHA256` | Uses Windows’ built-in tool to hash the file. |
| `findstr /v "hash"` | Filters out extra output, leaving just the hash line. |

Supported algorithms:

* `MD2`, `MD4`, `MD5`
    
* `SHA1`, `SHA256`, `SHA384`, `SHA512`
    

---

### 🧱 PowerShell Wrapper: Hash-String

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

```plaintext
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:

```plaintext
powershellCopyEditHash-String -InputString "foobar" -Algorithm SHA256
```

---

### 🧬 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.

---

### 🗂 Modular Profiles with `PSProfile.d`

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

```plaintext
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.

---

### 🏗 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
    

---

### 🔮 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.