Contents
Why You Should not compute a MAC using a symmetric key encryption method?
Using encryption alone makes your messages vulnerable to a ciphertext only attack. The sender, with the symmetric key, can encrypt the message and send E(M) . No one should be able to send a valid message other than the holder of the key.
Do hash functions use keys?
A hash function is a cryptographic algorithm which is used to transform large random size data to small fixed size data. The basic operation of hash functions does not need any key and operate in a one-way manner. The one-way operation means that it is impossible to compute the input from a particular output.
Which block is used in chaining in Mac?
In cryptography, a cipher block chaining message authentication code (CBC-MAC) is a technique for constructing a message authentication code from a block cipher.
Why is username authentication with symmetric keys important?
The Username Authentication with Symmetric Keys mechanism protects your application for integrity and confidentiality. Symmetric key cryptography relies on a single, shared, secret key that is used to both sign and encrypt a message, and is usually faster than public key cryptography. Server-Side Requirements
Is the authenticate then encrypt method secure?
The same applies to the encrypt-and-authenticate method used in SSH. On the positive side we show that the authenticate-then-encrypt method is secure if the encryption method in use is either CBC mode (with an underlying secure block cipher) or a stream cipher (that xor the data with a random or pseudorandom pad).
How should we assemble the encryption and the Mac?
There are some nifty encryption modes which include a MAC ( EAX, GCM …) but let’s assume that we are doing old-style crypto, so we have a standalone encryption method (e.g. AES with CBC chaining and PKCS#5 padding) and a standalone MAC (e.g. HMAC with SHA-256). How should we assemble the encryption and the MAC?
What are the three types of combining authentication and encryption?
It identifies 3 types of combining authentication (MAC) with encryption: Encrypt and Authenticate (E&A) used in SSH. It proves that EtA is the secure way to use, and both AtE and E&A are subject to attacks, unless the encryption method is either in CBC mode or it is a stream cipher.