A relatively short, say 24 to 40 bit, portion of the seed can be truly random to prevent tell-tale repetitions, but not long enough to prevent the attacker from recovering, say, a "randomly" produced key.
相对较短，比如24到40比特，种子可以是真正随机的，可以防止重复，但是并不足以防止攻击者恢复“随机”生成的密钥。