AES/GCM Interoperability
This page provides an information of a known issue and its proposed solution by adding a new default parameter interOp to the library.
A known issue in CADP for .NET Core that occurs when using a versioned key and Additional Authenticated Data (AAD) in AES/GCM Local mode, where the AUTH tag generated for Local mode and Remote mode is different, although the ciphertext remains the same.
The below table represents the scenarios that fail because of this issue.
| Encryption | Decryption | Remarks |
|---|---|---|
| Remote mode in CADP for .NetCore | Local mode in CADP for .NetCore | Decryption fails as the auth tags are different |
| Local mode in for CADP for .NET Core | Remote mode in CADP for .NET Core | Decryption fails as the auth tags are different |
| Local mode in for CADP for .NET Core | Any mode in any other connector | Decryption fails as the auth tags are different |
| Any mode in any other connector | Local mode in CADP for .NetCore | Decryption fails as the auth tags are different |
Solution
To resolve the above issue, a new default parameter interOp is added to the library for the Encrypt and Decrypt functions.
For every Encrypt operation, you need to set the interOp parameter as true else the encrypted text will not be compatible with:
CADP for .Net Core in remote mode of AES/GCM
Other connectors (in any mode)
The value of interOp parameter must be the same for both Encrypt and Decrypt operation. For example, if the value of interOp parameter is set to true during encryption, then it must be set to true in decryption also.
The Default value of the interOp parameter is set to false.
Note
If you encrypted the data using the old APIs in local mode, you must either set the InterOp parameter to false or omit it when decrypting the data.
Sample Code
byte[] tagVersionedKey = null;
// The last interOp parameter is set to true, in case you want the data to be decrypted using any other connector.
byte[] encDataVersionedKey = gcm.Encrypt(nonce, inputBytes, out tagVersionedKey, Encoding.ASCII.GetBytes(Default_AAD), true);
// As the interOp parameter is set to true while performing encryption operation, it must be set to true for decryption also, else the decryption will fail.
// Decrypting the encrypted data using Remote mode.
byte[] decDataVersionedKey = gcm.Decrypt(nonce, encDataVersionedKey, tagVersionedKey, Encoding.ASCII.GetBytes(Default_AAD), true);
