Analysis looks sound to me, using msg content to derive the key is generally bad form, especially messages are known to attackers and sent repeatedly. (eg. Hi)

Analysis looks sound to me, using msg content to derive the key is generally bad form, especially messages are known to attackers and sent repeatedly. (eg. Hi) It looks like a bunch of convoluted code that doesn't actually accomplish anything. Why is sha1_a = SHA1 (msg_key + substr (auth_key, x, 32)); sha1_b = SHA1 (substr (auth_key, 32+x, 16) + msg_key + substr (auth_key, 48+x, 16)); sha1_с = SHA1 (substr (auth_key, 64+x, 32) + msg_key); sha1_d = SHA1 (msg_key + substr (auth_key, 96+x, 32)); aes_key = substr (sha1_a, 0, 8) + substr (sha1_b, 8, 12) + substr (sha1_c, 4, 12); aes_iv = substr (sha1_a, 8, 12) + substr (sha1_b, 0, 8) + substr (sha1_c, 16, 4) + substr (sha1_d, 0, 8); better than sha1_a = SHA1 (msg_key + auth_key); sha1_b = SHA1 (sha1_a); sha1_с = SHA1 (sha1_b); sha1_d = SHA1 (sha1_C); aes_key = SHA1(sha1_a+sha1_b+sha1_c); aes_iv = SHA1(aes_key+sha1_d); and more importantly why is it better than aes_key = RANDOM aes_iv = RANDOM Are there special properties of the random bits of parts of various hashes that makes it more 'random'? To me it looks like repeatedly sending the same message, or a message whose hash varied by a few bits, would leak part of the auth key, basically the person probably doesn't know what they are doing and are just adding extra 'stuff' to assure themselves it's secure.