Cryptography Stack Exchange is a question and answer site for software developers, mathematicians and others interested in cryptography. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I am studying elliptic curves problems, which also includes study of related protocols such as ECIES. A there is a problem I don't understand operation $||$. What this operation mean?

Some stuff is mentioned on Wikipedia's Integration Encryption Scheme article, but this algoritm is better explain in book Guide to Elliptic Curves. This operation is mentioned in Alice's 3rd step:

$$ k_E || k_M = \operatorname{KDF}(S || S_1) $$

share|improve this question
up vote 4 down vote accepted

In terms of algorithms, it usually means concatenate - as in, join two binary (or otherwise defined) strings together (in this order). For wikipedia's cryptography articles that's nearly always the case.

When it is on the left side of an assignment, this means split the string from the right side into these component strings. This makes only sense if the length of most components is already fixed, of course – like here for the encryption and MAC keys.

In terms of programming languages such as C, however, it means logical or. Whilst it is unlikely the authors have confused them, it is something to be aware of.

share|improve this answer
Thanks, I know what it means in programming but in this context I have not seen it before , so If I understand it correctly, it works as simple join of Ke and Km? – eXPi May 16 '12 at 10:26
@eXPi yep. It also means, in this case, that the output of the KDF is split into two parts - one part for each key. – user46 May 16 '12 at 10:30

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.