Protocol specification

Name	Value	Semantics / Implementation-specific notes
session	iv|expiration|payload|mac	Encrypted message with metadata The value goes into acsSessionField.
iv	Fixed-length sequence of random bytes.	Initialization vector used to encrypt the message. The bytes are taken from RandomSource. The amount is determined by blockSize method of BlockCipher.
expiration	Fixed-length sequence of bytes.	Since when the cookies become expired. The time is calculated as result of getCurrentTime plus acsMaxAge and formatted using acsExpirationFormat.
payload	encrypt iv key (msg|padding)	Encrypted message (possibly with paddings).
msg	Sequence of bytes.	Original message. Serialized AuthCookieData value.
padding	Sequence of random bytes.	Suffix to the message to make it fit the cipher's requirements. The bytes are takes from RandomSource.
encrypt	A function.	Encryption algorithm. Specidied by acsEncryptAlgorithm.
mac	hash sk (iv|expiration|payload)	Message authentication code.
hash	A function.	Hashing algorithm. Specified by acsHashAlgorithm.
sk	Fixed-length sequence of random bytes.	A key, that is used for additional security and integrity checks. Got from ServerKeySet instance.
key	hash sk (iv|expiration)	A key, that is used to encrypt the message. The value is compared against cipherKeySize method of Cipher. Too long values are truncated, too short throw an exception.
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