Guessing or knowing the initial TCP sequence number (ISN) that a server will choose enables an attacker to establish a TCP connection. Please discuss if the following solutions are secure (to prevent hijacking etc.) against off-path attackers and why. [x]₃₂ denotes truncation of x to the 32 least significant bits. K is a (permanent) secret key stored locally and only known to the server. H represents a secure hash function (e.g., SHA256) and its algorithm is publicly known. Also note that || means concatenation and current timestamp is represented as UNIX timestamp. You can assume that 4 tuple information (source / destination IP and port) are known to the attacker. (1) Server selects ISN as ISN = [H(K)]₃₂.

(2) Server computes ISN as follows: ISN = [H(source IP address XOR destination IP address XOR current timestamp XOR K)]₃₂.

(3) Server computes ISN as ISN = [H(source IP address || destination IP address || source port number || destination port number || current timestamp)]₃₂.

(4) Server selects ISN using a standard (i.e., publicly-known) pseudo random generator with K as a seed.

(5) Server selects ISN as ISN = [AES ECB(K, counter)]₃₂, where the counter is continuous from the previous communication session.