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This is a common problem but the solutions suggested here and here don't work for me, also they don't involve a database.

I'd like the code sample 'Failing code (WITH database)' to work.

This is my encrypt/decrypt code (copied from here: https://msdn.microsoft.com/en-us/library/system.security.cryptography.aes.aspx?cs-save-lang=1&cs-lang=vb&f=255&MSPPError=-2147217396#code-snippet-2):

Shared Function EncryptStringToBytes_Aes(ByVal plainText As String, ByVal Key() As Byte, ByVal IV() As Byte) As Byte() ' Check arguments. If plainText Is Nothing OrElse plainText.Length <= 0 Then Throw New ArgumentNullException("plainText") End If If Key Is Nothing OrElse Key.Length <= 0 Then Throw New ArgumentNullException("Key") End If If IV Is Nothing OrElse IV.Length <= 0 Then Throw New ArgumentNullException("Key") End If Dim encrypted() As Byte ' Create an Aes object ' with the specified key and IV. Using aesAlg As Aes = Aes.Create() aesAlg.Key = Key aesAlg.IV = IV ' Create a decrytor to perform the stream transform. Dim encryptor As ICryptoTransform = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV) ' Create the streams used for encryption. Using msEncrypt As New MemoryStream() Using csEncrypt As New CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write) Using swEncrypt As New StreamWriter(csEncrypt) 'Write all data to the stream. swEncrypt.Write(plainText) End Using encrypted = msEncrypt.ToArray() End Using End Using End Using ' Return the encrypted bytes from the memory stream. Return encrypted End Function 'EncryptStringToBytes_Aes Shared Function DecryptStringFromBytes_Aes(ByVal cipherText() As Byte, ByVal Key() As Byte, ByVal IV() As Byte) As String ' Check arguments. If cipherText Is Nothing OrElse cipherText.Length <= 0 Then Throw New ArgumentNullException("cipherText") End If If Key Is Nothing OrElse Key.Length <= 0 Then Throw New ArgumentNullException("Key") End If If IV Is Nothing OrElse IV.Length <= 0 Then Throw New ArgumentNullException("Key") End If ' Declare the string used to hold ' the decrypted text. Dim plaintext As String = Nothing ' Create an Aes object ' with the specified key and IV. Using aesAlg As Aes = Aes.Create() aesAlg.Key = Key aesAlg.IV = IV ' Create a decrytor to perform the stream transform. Dim decryptor As ICryptoTransform = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV) ' Create the streams used for decryption. Using msDecrypt As New MemoryStream(cipherText) Using csDecrypt As New CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read) Using srDecrypt As New StreamReader(csDecrypt) ' Read the decrypted bytes from the decrypting stream ' and place them in a string. plaintext = srDecrypt.ReadToEnd() End Using <= PADDING ERROR THROWN HERE End Using 'cipherText = msDecrypt.ToArray() 'added by me End Using End Using Return plaintext End Function 'DecryptStringFromBytes_Aes

Working sample (without database)

 Dim original As String = "Here is some data to encrypt!" Dim key As Rfc2898DeriveBytes = New Rfc2898DeriveBytes(_sharedSecret, _salt) Try ' Create a new instance of the Aes ' class. This generates a new key and initialization ' vector (IV). Using myAes As Aes = Aes.Create() myAes.Key = key.GetBytes(myAes.KeySize / 8) myAes.IV = key.GetBytes(myAes.BlockSize / 8) ' Encrypt the string to an array of bytes. Dim encrypted As Byte() = EncryptStringToBytes_Aes(original, myAes.Key, myAes.IV) ' Decrypt the bytes to a string. Dim roundtrip As String = DecryptStringFromBytes_Aes(encrypted, myAes.Key, myAes.IV) 'Display the original data and the decrypted data. ltStatus.Text = String.Format("Original: {0}", original) ltStatus.Text += String.Format("Round Trip: {0}", roundtrip) End Using Catch ex As Exception Console.WriteLine("Error: {0}", ex.Message) End Try

Failing code (WITH database)

 Dim _salt As Byte() = Encoding.ASCII.GetBytes("o6806642kbM7c5") Dim _sharedSecret As String = "abcd" Dim original As String = "Here is some data to encrypt!" Dim key As Rfc2898DeriveBytes = New Rfc2898DeriveBytes(_sharedSecret, _salt) Dim encrypted As Byte() Try Using myAes As Aes = Aes.Create() myAes.Key = key.GetBytes(myAes.KeySize / 8) myAes.IV = key.GetBytes(myAes.BlockSize / 8) myAes.Padding = PaddingMode.PKCS7 encrypted = EncryptStringToBytes_Aes(original, myAes.Key, myAes.IV) End Using Catch ex As Exception Console.WriteLine("Error: {0}", ex.Message) End Try 'save to DB Dim myConnection As SqlConnection = GetConnection() Dim cmd As New SqlCommand("UPDATE banks set bank_name=@bankname WHERE id=1", myConnection) cmd.Parameters.Add(New SqlParameter("@bankname", encrypted)) Try myConnection.Open() cmd.ExecuteScalar() Catch ex As Exception GlobalFunctions.LogError("banks:INSERT encrypted", ex.Message, LogLevel.Normal) Finally myConnection.Close() End Try 'retreive from db Dim decrypted As String = "" myConnection = GetConnection() cmd = New SqlCommand("SELECT bank_name FROM banks where id=1", myConnection) Dim reader As SqlDataReader Try myConnection.Open() reader = cmd.ExecuteReader If reader.Read Then Using myAes As Aes = Aes.Create() myAes.Key = key.GetBytes(myAes.KeySize / 8) myAes.IV = key.GetBytes(myAes.BlockSize / 8) myAes.Padding = PaddingMode.PKCS7 decrypted = DecryptStringFromBytes_Aes(reader("bank_name"), myAes.Key, myAes.IV) End Using Else GlobalFunctions.LogError("banks:nothing to be read?!?", LogLevel.Normal) End If Catch ex As Exception GlobalFunctions.LogError("banks:SELECT encrypted.", ex.Message, LogLevel.Normal) Finally myConnection.Close() End Try

But something goes wrong here:

A binary value is succesfully added in my MSSQL database in field bank_name of type varbinary(MAX). (I also tried smaller fields, e.g. varbinary(50))

But when I try to decrypt this field after retreival from the database I get the error Padding is invalid and cannot be removed. See the codeline with the comment '<= PADDING ERROR THROWN HERE' in the above code 'Failing code (WITH database)'.

I checked here and here. And I'm not passing an empty string Also I tried adding cipherText = msDecrypt.ToArray(), but the error already occurs before this line is hit.

UPDATE 2

My dumped values are:

ReportError stores the values in a textfield in the DB, the reported values are:

myAes.Key in
00000000 95 0C 95 EA 1D 40 0C FB 1D 3F B7 FB 73 FB 3F EA ���������������� 00000010 40 62 51 62 51 EA 62 73 B7 2E 1D C8 1D 51 51 95 ����������������

myAes.IV in
00000000 51 A6 84 73 95 C8 2E 62 84 C8 0C 62 C8 2E 1D 84 ����������������

encrypted in
00000000 FB FB B7 73 D9 51 A6 2E 95 73 62 73 3F 84 A6 40 ���������������� 00000010 B7 62 84 2E 51 95 EA 1D 51 A6 EA 2E 51 A6 51 95 ����������������

myAes.Key out
00000000 51 1D 73 40 EA A6 73 EA FB 73 73 A6 0C A6 D9 1D ���������������� 00000010 2E 3F FB 2E 73 A6 A6 0C A6 C8 95 0C D9 1D B7 73 ����������������

myAes.IV out
00000000 B7 95 51 73 B7 D9 95 EA 0C C8 95 95 0C 84 40 62 ����������������

encrypted out
00000000 FB FB B7 73 D9 51 A6 2E 95 73 62 73 3F 84 A6 40 ���������������� 00000010 B7 62 84 2E 51 95 EA 1D 51 A6 EA 2E 51 A6 51 95 ����������������

banks:SELECT encrypted. Padding is invalid and cannot be removed.

Here's the full code I use now:

Imports System.Security.Cryptography Imports System.Data.SqlClient Imports System.Text Namespace HexDump Class Utils Public Shared Function HexDump(bytes As Byte(), Optional bytesPerLine As Integer = 16) As String If bytes Is Nothing Then Return "<null>" End If Dim bytesLength As Integer = bytes.Length Dim HexChars As Char() = "0123456789ABCDEF".ToCharArray() ' 8 characters for the address Dim firstHexColumn As Integer = 8 + 3 ' 3 spaces ' - 2 digit for the hexadecimal value and 1 space ' - 1 extra space every 8 characters from the 9th Dim firstCharColumn As Integer = firstHexColumn + bytesPerLine * 3 + (bytesPerLine - 1) / 8 + 2 ' 2 spaces ' - characters to show the ascii value Dim lineLength As Integer = firstCharColumn + bytesPerLine + Environment.NewLine.Length ' Carriage return and line feed (should normally be 2) Dim line As Char() = (New [String](" "c, lineLength - Environment.NewLine.Length) + Environment.NewLine).ToCharArray() Dim expectedLines As Integer = (bytesLength + bytesPerLine - 1) / bytesPerLine Dim result As New StringBuilder(expectedLines * lineLength) Dim i As Integer = 0 While i < bytesLength line(0) = HexChars((i >> 28) And &HF) line(1) = HexChars((i >> 24) And &HF) line(2) = HexChars((i >> 20) And &HF) line(3) = HexChars((i >> 16) And &HF) line(4) = HexChars((i >> 12) And &HF) line(5) = HexChars((i >> 8) And &HF) line(6) = HexChars((i >> 4) And &HF) line(7) = HexChars((i >> 0) And &HF) Dim hexColumn As Integer = firstHexColumn Dim charColumn As Integer = firstCharColumn For j As Integer = 0 To bytesPerLine - 1 If j > 0 AndAlso (j And 7) = 0 Then hexColumn += 1 End If If i + j >= bytesLength Then line(hexColumn) = " "c line(hexColumn + 1) = " "c line(charColumn) = " "c Else 'Dim b As Byte = bytes(i + j) 'line(hexColumn) = HexChars((b >> 4) And &HF) 'line(hexColumn + 1) = HexChars(b And &HF) 'line(charColumn) = (If(b < 32, "·"c, CChar(b))) Dim b As Byte = bytes((i + j)) line(hexColumn) = HexChars(((b + 4) _ And 15)) line((hexColumn + 1)) = HexChars((b And 15)) line(charColumn) = Microsoft.VisualBasic.ChrW(65533) End If hexColumn += 3 charColumn += 1 Next result.Append(line) i += bytesPerLine End While Return result.ToString() End Function End Class End Namespace Public Class banks_financial Inherits System.Web.UI.Page Private _lang As String Private _registryId As Integer Private _salt As Byte() = Encoding.ASCII.GetBytes("o6806642kbM7c5") Private _sharedSecret As String = "abcd" Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load Dim original As String = "Here is some data to encrypt!" Dim key As Rfc2898DeriveBytes = New Rfc2898DeriveBytes(_sharedSecret, _salt) Dim encrypted As Byte() Try Using myAes As Aes = Aes.Create() myAes.Key = key.GetBytes(myAes.KeySize / 8) myAes.IV = key.GetBytes(myAes.BlockSize / 8) myAes.Padding = PaddingMode.PKCS7 encrypted = EncryptStringToBytes_Aes(original, myAes.Key, myAes.IV) ReportError("myAes.Key in", HexDump.Utils.HexDump(myAes.Key)) ReportError("myAes.IV in", HexDump.Utils.HexDump(myAes.IV)) ReportError("encrypted in", HexDump.Utils.HexDump(encrypted)) End Using Catch ex As Exception Console.WriteLine("Error: {0}", ex.Message) End Try 'save to DB Dim myConnection As SqlConnection = GetConnection() Dim cmd As New SqlCommand("UPDATE banks set bank_name=@bankname WHERE id=1", myConnection) cmd.Parameters.Add(New SqlParameter("@bankname", encrypted)) Try myConnection.Open() cmd.ExecuteScalar() Catch ex As Exception GlobalFunctions.ReportError("banks:INSERT encrypted", ex.Message, LogLevel.Normal) Finally myConnection.Close() End Try 'retreive from db Dim decrypted As String = "" myConnection = GetConnection() cmd = New SqlCommand("SELECT bank_name FROM banks where id=1", myConnection) Dim reader As SqlDataReader Try myConnection.Open() reader = cmd.ExecuteReader If reader.Read Then Using myAes As Aes = Aes.Create() myAes.Key = key.GetBytes(myAes.KeySize / 8) myAes.IV = key.GetBytes(myAes.BlockSize / 8) myAes.Padding = PaddingMode.PKCS7 ReportError("myAes.Key out", HexDump.Utils.HexDump(myAes.Key)) ReportError("myAes.IV out", HexDump.Utils.HexDump(myAes.IV)) ReportError("encrypted out", HexDump.Utils.HexDump(reader("bank_name"))) decrypted = DecryptStringFromBytes_Aes(reader("bank_name"), myAes.Key, myAes.IV) ReportError("decrypted", decrypted) End Using Else GlobalFunctions.ReportError("banks:nothing to be read?!?", LogLevel.Normal) End If Catch ex As Exception GlobalFunctions.ReportError("banks:SELECT encrypted.", ex.Message, LogLevel.Normal) Finally myConnection.Close() End Try ltStatus.Text = GetMessageStatus(decrypted, MsgType.ok) End Class
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    is there a reason you are using PBKDF2 for the PW? The salt for those should be different as should be IV for each encryption. Using the same ones over and over defeats the purpose (crack one and they are all cracked). Using different ones means saving them somewhere. Commented Apr 15, 2016 at 18:22
  • Hi, thanks. I assume you mean PKCS7? Not really, I saw it recommended in another post. Could I omit padding altogether or what would you recommend? Also, the salt will be different per user in a real-life scenario (probably their userid or date the account was created). Commented Apr 15, 2016 at 18:42
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    No, Rfc2898DeriveBytes is for password-based key derivation functionality or PBKDF. The way you have it constructed. to do it right means also saving a unique IV and the Salt for each item. I am trying to figure out how much of what is there is trial and error remnants versus actually required. Commented Apr 15, 2016 at 18:48
  • Is there only one app ever reading and writing to the DB, or will there be other app instances in other locations reading the info? Commented Apr 15, 2016 at 19:40
  • There will be only one app reading and writing to the DB indeed. Commented Apr 15, 2016 at 19:46

2 Answers 2

Reset to default
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The immediate problem is that your test code is misusing Rfc2898DeriveBytes/ PBKDF. It has nothing to do with the database. Each time you call GetBytes() on a given instance, it returns a different set of bytes (by design!). This is apparent with a bit of code like this:

 Dim salt = CryptoTools.GetRandomBytes(16) Dim PBKDF = New Rfc2898DeriveBytes("secret", salt, 10000) Dim a = PBKDF.GetBytes(32) Dim b = PBKDF.GetBytes(32) Dim c = PBKDF.GetBytes(32) If a.SequenceEqual(b) = False Then Console.WriteLine("A != B") End If ...

It's very clear with Intellisense:

enter image description here

The arrays are not at all alike. From the Remarks section on MSDN for GetBytes:

The Rfc2898DeriveBytes class takes a password, a salt, and an iteration count, and then generates keys through calls to the GetBytes method. Repeated calls to this method will not generate the same key; ...

The emphasis is mine, but is intended to point out that it is a key generator not just a hasher. So, in your "Fails with Database" code you have this block:

Dim key As Rfc2898DeriveBytes = New Rfc2898DeriveBytes(_sharedSecret, _salt) ... Using myAes As Aes = Aes.Create() ... myAes.Key = key.GetBytes(myAes.KeySize / 8) myAes.IV = key.GetBytes(myAes.BlockSize / 8) ... End Using

The Key and IV generated will not be the same. This is good, but probably not what you intended. The same block is used later to decrypt what was read back from the db. The Key and IV used to decrypt will also be different from each other, but more importantly they will not be the same Key and IV used to encrypt!

This is a fatal flaw, and causes the error. It seems like a misleading error message, but it is simple to reproduce/fix. You need a new PBKDF to 'start over' in the decryption part, or Reset the existing one:

' after this line... Dim decrypted As String = "" ' ...add this: key As Rfc2898DeriveBytes = New Rfc2898DeriveBytes(_sharedSecret, _salt) ' or 'key.Reset()

It is more likely that the real code would not be doing a roundtrip in the same method, and using a new Rfc2898DeriveByteswould be created.

Finally, note that the IV and Salt should be unique and random for effective encryption. There really isn't much point in encrypting each row with the same password, key, salt and IV beyond the illusion of security. Someone only has to crack the PW for one row to get the data for all the rows.

Because Rfc2898DeriveBytes is deterministic, it can play a role in generating the IV and Salt (for the data to be encrypted) without having to save them or use static ones.

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8 Comments

@Flo This is the answer. You can't reuse an instance of Rfc2898DeriveBytes for both your encrypt and decrypt operation. There are other issues which have already been pointed out (like the way IVs are generated), but this addresses the decryption issue.
@Flo In your sample code for Update 2, what happens if you add key.Reset() before the decrypt operation (maybe after the 'retreive from db' comment)?
Yes, Reset will work as well, even if you are not using the default number of iterations. Typically though, the read code would be in different method than the write and likely create a new instance. I personally would not use a global instance.
If it solves your problem, please click the checkmark and upvote it. Whether that is secure depends on what you are protecting against. A single password for Rfc2898DeriveBytes, fixed Salt and the default number of iterations means you are creating the same Key, IV pair for each row. Something needs to vary for it to be effective. And with the pass/secret and salt hardcoded, the answer is right there in the code if that gets stolen.
Assuming multiple users, it means every row for UserA will use the same encryption Key and IV, which is not secure. This can be fixed by using other than the default iterations for Rfc2898DeriveBytes; the default is 1000 but 10,000 is more common. If you used a random number, you could get a different Key/IV set for each row even using the same user id. It is very hard to define what would be the right way via comments given I have no idea what the app does or what you are protecting against.
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Generally a padding error really means that the key, encrypted data or options are incorrect, not the padding, per se.

Make sure the key is exactly the correct length, if not the implementation will use unspecified bytes. Make the key exactly a correct key size: 128, 192 or 256 bits (16, 24 or 32 bytes).

Make sure the key, data and IV do not have an incorrect encoding, encryption is based on 8-bit bytes with no encoding. Some libraries will accept and produce other encodings such as Base64 and hexadecimal, check the documentation carefully.

Hex dump the key, IV, encrypted data and decrypted data and add samples of these to the question.

Encryption function calls are actually simple, if you supply the correct (and full) inputs the output will be correct. If the results check the inputs carefully.

UPDATE:
The IV and key are not the same for both encryption and decryption, they must be the same.

One way to ensure the IV is the same is to pre-pend it to the encrypted data on encryption and on decryption recover it from the encrypted data and skip it when decryption the encrypted data.

The key must be pre-shared between the encryption and decryption code in some manner prior to the decryption.

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5 Comments

I've added a bounty on this question, perhaps you can help? I see you've updated your answer. But I still don't know how to approach implementing your solution. I'm new to encryption so do you perhaps have a code sample of what you're suggesting? And how do I know if the key is exactly the correct length? Thanks!
What part do you not understand?
Why my code is not working the moment a database is involved.
Best guess is that the db field is not specified correctly. Hex dump the key, IV, original data, encrypted data going to the db, encrypted data from the database and decrypted data. The reasons for the hex dumps is that the original data may not be what you think it is, it may be UTF-16 encoded or some other encoding. The reason for before and after the db is to ensure the db is not corrupting it, perhaps because of a inappropriate field type. Key is if the data going into the db is the same as coming out. You will have to debug your code, the above is a good start.
Thanks! I updated my code (see update 2 for a full working code sample) with the dumps (I hope I did it right). And it looks indeed as if the values are different in than out values. What would you recommend as next steps?

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