Possible bug around Org.BouncyCastle.Crypto.Fips.FipsAes.Service and Org.BouncyCastle.Crypto.BlockCipherBuilderImpl<Org.BouncyCastle.Crypto.Fips.FipsAes.ParametersWithIV>

[vitali-pr]

I don't have an easy and straightforward way to reproduce so don't file a bug. Though it seems to be something wrong there.
I have a following code for aes encryption/decryption:

public byte[] ProcessBlock(byte[] inp, int inpOff, int inpLen, bool forEncryption, byte[] key, byte[] initVector) {
    FipsAes.Key aesKey = new FipsAes.Key(key);
    IBlockCipherBuilder<IParameters<Algorithm>> cipherBuilder = createBuilder(forEncryption, aesKey, initVector);
    MemoryOutputStream memoryStream = new MemoryOutputStream();
    IBlockCipher blockCipher = cipherBuilder.BuildBlockCipher(memoryStream);
    if (inpLen % blockCipher.BlockSize != 0) {
        throw new ArgumentException("Not multiple of block: " + inpLen);
    }
    
    using (Stream stream = blockCipher.Stream) {
        stream.Write(inp, inpOff, inpLen);
    }
    return memoryStream.ToArray();
}

private static IBlockCipherBuilder<IParameters<Algorithm>> createBuilder(bool forEncryption, FipsAes.Key aesKey, byte[] initVector) {
    IBlockCipherService provider = CryptoServicesRegistrar.CreateService<IBlockCipherService>(
        (ICryptoServiceType<IBlockCipherService>) aesKey);
    IBlockCipherBuilder<IParameters<Algorithm>> cipherBuilder;
    if (forEncryption) {
        cipherBuilder = provider.CreateBlockEncryptorBuilder<FipsAes.ParametersWithIV>(FipsAes.Cbc.WithIV(initVector));
    } else {
        cipherBuilder = provider.CreateBlockDecryptorBuilder<FipsAes.ParametersWithIV>(FipsAes.Cbc.WithIV(initVector));
    }

    return cipherBuilder;
}

It all works as expected. Application is heavily doing encryption/decryption (mostly encryption) calls for some data (16 bytes everywhere AFAICT).
But sometimes under heavy conditions (huge CPU/memory usage) it produces different result for the same input data. You might notice that 2 bc fips calls are moved to a separate method createBuilder. If I disable optimization by using
[MethodImplAttribute(MethodImplOptions.NoOptimization)]
for that 1 method, the issue is not reproducible anymore.

Does it sound familiar to anyone?