Aes Encryption using powershell.

PowershellAes.ps1

function Create-AesManagedObject($key, $IV) {
    $aesManaged = New-Object "System.Security.Cryptography.AesManaged"
    $aesManaged.Mode = [System.Security.Cryptography.CipherMode]::CBC
    $aesManaged.Padding = [System.Security.Cryptography.PaddingMode]::Zeros
    $aesManaged.BlockSize = 128
    $aesManaged.KeySize = 256
    if ($IV) {
        if ($IV.getType().Name -eq "String") {
            $aesManaged.IV = [System.Convert]::FromBase64String($IV)
        }
        else {
            $aesManaged.IV = $IV
        }
    }
    if ($key) {
        if ($key.getType().Name -eq "String") {
            $aesManaged.Key = [System.Convert]::FromBase64String($key)
        }
        else {
            $aesManaged.Key = $key
        }
    }
    $aesManaged
}

function Create-AesKey() {
    $aesManaged = Create-AesManagedObject
    $aesManaged.GenerateKey()
    [System.Convert]::ToBase64String($aesManaged.Key)
}

function Encrypt-String($key, $unencryptedString) {
    $bytes = [System.Text.Encoding]::UTF8.GetBytes($unencryptedString)
    $aesManaged = Create-AesManagedObject $key
    $encryptor = $aesManaged.CreateEncryptor()
    $encryptedData = $encryptor.TransformFinalBlock($bytes, 0, $bytes.Length);
    [byte[]] $fullData = $aesManaged.IV + $encryptedData
    $aesManaged.Dispose()
    [System.Convert]::ToBase64String($fullData)
}

function Decrypt-String($key, $encryptedStringWithIV) {
    $bytes = [System.Convert]::FromBase64String($encryptedStringWithIV)
    $IV = $bytes[0..15]
    $aesManaged = Create-AesManagedObject $key $IV
    $decryptor = $aesManaged.CreateDecryptor();
    $unencryptedData = $decryptor.TransformFinalBlock($bytes, 16, $bytes.Length - 16);
    $aesManaged.Dispose()
    [System.Text.Encoding]::UTF8.GetString($unencryptedData).Trim([char]0)
}


$encrypt_or_decrypt =  Read-Host -Prompt "encrypt or decrypt? [e/d]"

if($encrypt_or_decrypt -eq "e"){
    #generate key
    $key = Create-AesKey
    Write-Host "key: $key"

    #ask for string to encrypt
    $unencryptedString = Read-Host "Encrypt this"

    #encrypt it, pipe to clipboard
    $encryptedString = Encrypt-String $key $unencryptedString 
    $encryptedString | Set-Clipboard

} elseif ($encrypt_or_decrypt -eq "d") {
    #ask for encrypted string and key
    $encryptedString = Read-Host "decrypt this"
    $key = Read-Host "key"

    #decrypt it, pipe to clipboard
    try {
        $backToPlainText = Decrypt-String $key $encryptedString
        $backToPlainText | Set-Clipboard
    } catch {
        Write-Host "Invalid"
    }


}

19May2019:
Added interactive prompt for encryption/decryption