Implement support for HMACs to provide another way for message authentication, integrity checking and everything else provided by signatures.

Hint: Possible interface to support is  System.Security.Cryptography.KeyedHashAlgorithm

Implement (different?) shuffle algorithms for shuffling collections.

At least Fisher-Yates shuffle.

There is currently no support for handling keys like the AsymmetricCiphers ToEncryptedXmlString/FromEncryptedXmlString methods provide.

The "packer" should be able to en/decrypt the symmetric key using public and private key cryptography.

Add support for the symmetrical one-time pad.

The current GenericHasher creates a new instance every time it is used. This is not great performance-wise.

Implement a new class for hashing, likewise SymmetricCipher.

Cipha lacks support of ECDiffieHellman key exchange

Implement a AsymmetricCipher using the Cipher base class.

Implement different factories, each providing different levels of secure ciphers.

Add support to en/decrypt/process large amount of data asynchronously.

The ECDiffieHellmanCipher only supports hash based key derivations.
TLS and HMAC support should be implemented.

Check performance and find bottlenecks

When passing a reference to another cipher (AesManaged or similar), one should be able to specify if the reference shall also be disposed.

The IV is currently derived from the password and salt.
It should be generated randomly (via RNGCryptoServiceProvider).