🪟 PowerShell Base64 Encode & Decode

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🪟 PowerShell Base64 Encode & Decode

Transfer files without using the network — especially in red-team or penetration testing situations. If you've got terminal access, this method lets you convert a file to Base64, move the string manually (like copy-paste ✂️📋), and decode it on the other side!

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✅ Step 1: Verify File Integrity with md5sum 🧬

Before and after transferring the file, generate the MD5 hash to verify it later once transfered

md5sum id_rsa

🟢 Output:

4e301756a07ded0a2dd6953abf015278  id_rsa

This is your "file fingerprint" 🔍 — it should match after the transfer.

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🔄 Step 2: Encode File to Base64 on Linux 🧾➡️🔡

cat id_rsa | base64 -w 0; echo

📋 This gives you a Base64 string of your file — copy it all!

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

⚠️ Make sure you use -w 0 so there's no line break!

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🪟 Step 3: Decode Base64 in PowerShell 🖥️

Paste your Base64 string into this PowerShell command to recreate the file:

[IO.File]::WriteAllBytes("C:\Users\Public\id_rsa", [Convert]::FromBase64String("PASTE-YOUR-BASE64-HERE"))

💾 This writes the file back in its original form!

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🔐 Step 4: Confirm the File Integrity (again)

Now check the hash on Windows to confirm the file was transferred correctly:

Get-FileHash C:\Users\Public\id_rsa -Algorithm md5

✅ If the hash matches 4E301756A07DED0A2DD6953ABF015278 — mission accomplished! 🎉

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⚠️ Notes & Limitations 🚧

• 🪟 cmd.exe has a max string limit of 8191 characters

• 🕸️ Some web shells can error if strings are too long

• 🧩 For large files, consider other tools (like certutil, bitsadmin, etc.)

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This method is perfect for small files like:

• SSH keys

• Scripts

• Tiny DLLs

Let me know if you'd like a PowerShell script version or to automate hash checks! 💻✨