When attempting to decrypt the Windows administrator password on AWS EC2, you might encounter two particularly frustrating errors:

Error 1: "Private key must begin with '-----BEGIN RSA PRIVATE KEY-----' and end with '-----END RSA PRIVATE KEY-----'"
Error 2: "There was an error decrypting your password. Please ensure that you have entered your private key correctly"

From hands-on experience with AWS EC2 Windows instances, these issues typically stem from:

• Key format incompatibility (especially with OpenSSH format keys)
• Incorrect line endings in the private key file
• Hidden characters or encoding issues
• Mismatch between the key pair used for launch and decryption

If you're using OpenSSH format keys (common with modern ssh-keygen), you'll need to convert them to PEM format:

# Convert OpenSSH private key to PEM format
ssh-keygen -p -m PEM -f your_private_key.ppk

# Verify the key structure
cat your_private_key.pem | head -n 1
# Should output: -----BEGIN RSA PRIVATE KEY-----

For Windows users, here's a PowerShell script to validate your key file:

function Test-PrivateKeyFormat {
    param (
        [string]$KeyPath
    )
    
    $content = Get-Content $KeyPath -Raw
    if (-not $content.StartsWith('-----BEGIN RSA PRIVATE KEY-----')) {
        Write-Error "Invalid private key header"
        return $false
    }
    
    if (-not $content.EndsWith("-----END RSA PRIVATE KEY-----n")) {
        Write-Warning "Key might have line ending issues"
        # Try normalizing line endings
        $content = $content.Trim() + "n"
        Set-Content -Path $KeyPath -Value $content -NoNewline
    }
    
    return $true
}

# Usage:
Test-PrivateKeyFormat -KeyPath "C:\path\to\your\key.pem"

AWS's decryption service is particularly sensitive to:

• Exactly one newline after the header
• Exactly one newline before the footer
• No trailing whitespace

Use this sed command (Linux/Mac) to normalize the key:

sed -i '' -e '$a\' your_key.pem

If you've exhausted all key format options, consider these steps:

1. Create an AMI of the problematic instance
2. Launch a new instance from the AMI with a new key pair
3. Retrieve the password using the new key pair
4. Attach the original volume to the new instance if data recovery is needed

To avoid this issue in future deployments:

# Generate AWS-compatible keys from the start
ssh-keygen -m PEM -t rsa -b 4096 -f aws_key

# Store the key with proper permissions
chmod 400 aws_key.pem

# Verify fingerprint matches AWS console
openssl pkcs8 -in aws_key.pem -inform PEM -outform DER -topk8 -nocrypt | openssl sha1 -c

Remember that AWS EC2 Windows password decryption only works with RSA private keys - ED25519 and other modern formats won't work with this specific feature.

---

When launching a Windows EC2 instance using a pre-existing key pair, many developers encounter the frustrating scenario where the instance boots successfully but the administrator password refuses to decrypt - even with the correct private key. The error messages typically show either format validation failures or generic decryption errors.

First, verify your private key structure matches AWS's strict requirements:

-----BEGIN RSA PRIVATE KEY-----
BASE64 ENCODED KEY CONTENT
-----END RSA PRIVATE KEY-----

Common formatting issues include:

• Extra whitespace or blank lines
• Missing header/footer markers
• Incorrect line endings (CRLF vs LF)
• PEM vs OpenSSH format confusion

If your key is in OpenSSH format, convert it to PEM format:

ssh-keygen -p -m PEM -f private_key.ppk

For PuTTY .ppk files, use PuTTYgen to export as OpenSSH format first, then convert to PEM.

Here's a Python script to validate key format:

import OpenSSL.crypto

def validate_private_key(key_path):
    try:
        with open(key_path, 'r') as key_file:
            key_data = key_file.read()
        OpenSSL.crypto.load_privatekey(OpenSSL.crypto.FILETYPE_PEM, key_data)
        return True
    except Exception as e:
        print(f"Key validation failed: {str(e)}")
        return False

When uploading keys through AWS console or CLI:

• Ensure no extraneous characters exist
• Verify the MD5 fingerprint matches your local key
• Check IAM permissions for EC2 key operations
• Confirm regional consistency between keypair and instance

If web console decryption fails, try AWS CLI:

aws ec2 get-password-data \
    --instance-id i-1234567890abcdef0 \
    --priv-launch-key ~/.ssh/my-key-pair.pem \
    --output text

Enable CloudTrail logging to monitor decryption attempts:

aws cloudtrail lookup-events \
    --lookup-attributes AttributeKey=EventName,AttributeValue=GetPasswordData

Check for password generation issues via instance metadata:

Invoke-RestMethod -uri http://169.254.169.254/latest/meta-data/password

Consider these last-resort options:

• Create a new key pair and associate with instance
• Use EC2SerialConsole for direct access
• Attach the volume to another instance for manual password reset