VB.NET AES错误“填充无效且无法删除”相同的密钥/ iv和最终块刷新

Question

我使用AesCryptoServiceProvider来使用AES执行加密和解密。 加密似乎有效，但解密会抛出一个异常，说“填充无效，无法删除”。

这是我的代码：

Public Function AESEnc(ByVal plain As String, ByVal key As String, ByVal iv As String) As AesResult
    Dim ciphertext As String
    Dim k(31) As Byte
    Dim v(15) As Byte
    Dim ret As AesResult
    Dim pBytes As Byte() = StrToByteArray(plain)
    Dim cipher As New AesCryptoServiceProvider()
    Dim enc As ICryptoTransform
    Dim ms As New MemoryStream
    Dim cs As CryptoStream

    k = StrToByteArray(key)
    v = HexStringByteArrayConverter.HexStringToBytes(iv)
    cipher.Mode = CipherMode.CFB
    cipher.Padding = PaddingMode.PKCS7

    enc = cipher.CreateEncryptor(k, v)
    cs = New CryptoStream(ms, enc, CryptoStreamMode.Write)
    cs.Write(pBytes, 0, pBytes.Length)
    cs.FlushFinalBlock()
    cs.Close()
    ciphertext = HexStringByteArrayConverter.BytesToHexString(ms.ToArray())
    ret.data = ciphertext
    ret.iv = v
    ret.key = k

    Return ret
End Function 'AESEnc

Public Function AESDec(ByVal ciphertext As String, ByVal key As String, ByVal iv As String) As AesResult
    Dim plaintext As String
    Dim k(31) As Byte
    Dim v(15) As Byte
    Dim ret As AesResult
    Dim pBytes As Byte() = StrToByteArray(ciphertext)
    Dim cipher As New AesCryptoServiceProvider()
    Dim dec As ICryptoTransform
    Dim ms As New MemoryStream
    Dim cs As CryptoStream

    k = StrToByteArray(key)
    v = HexStringByteArrayConverter.HexStringToBytes(iv)
    cipher.Mode = CipherMode.CFB
    cipher.Padding = PaddingMode.PKCS7

    dec = cipher.CreateDecryptor(k, v)
    cs = New CryptoStream(ms, dec, CryptoStreamMode.Write)
    cs.Write(pBytes, 0, pBytes.Length)
    cs.FlushFinalBlock()
    cs.Close()
    plaintext = ByteArrayToString(ms.ToArray())
    ret.data = plaintext
    ret.iv = v
    ret.key = k

    Return ret
End Function 'AESDec