On 5 August 2015 22:35:10 CEST, Florian Weimer <f...@deneb.enyo.de> wrote: >Suppose I have a sequence of words over some alphabet, and I want to >compute a cryptographically secure hash over that. Simply >concatenating the hashes to form a single word does not work because >the word boundaries might have been meaningful and not implicit in the >inputs, and then you have second preimages etc. I guess this is why >we have DER, among other reasons.
Isn't the normal way to effectively introduce an alphabet A' that is a superset of A plus a word separator? You know like A=a-z A'=A+ space? And/or introduce groupings - but that should be equivalent (eg: you want to send arbitrary length bit-string "words", so you decide to treat the 8 first bits as word length in binary, possibly with 8th bit as signal for word longer than 127 bits; new 8 bit length field before word...). In the first case you need a hash function over A' rather than A; In both you need a decode step to get back to either words in A or extracting the bitstrings you wanted? >I've been asked to provide some citation for this observation, but I >can't find a proper reference. Any suggestions? Isn't this trivial? {a,aa} != {aaa} ? Apologies if I'm completely missing your point. Best regards, Eirik S _______________________________________________ cryptography mailing list cryptography@randombit.net http://lists.randombit.net/mailman/listinfo/cryptography