vb.net - VB.NET AESエラー「パディングが無効で削除できません」同じキー/ivと最終ブロックがフラッシュされました

Question

AES を使用して暗号化と復号化を実行するために、AesCryptoServiceProvider を使用します。暗号化は機能しているようですが、復号化すると「パディングが無効であり、削除できません」という例外がスローされます。

これが私のコードです：

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