HMAC(K,C) = SHA1(K ⊕ 0x5c5c… ∥ SHA1(K ⊕ 0x3636… ∥ C))

The basic idea I get and I'm thinking means something like plus. What are the two vertical lines. (K is a pre-defined but arbitrary value and C is a counter.)

The wikipedia math symbol page is helping much

I'm afraid you will need to give more information. What field is this equation from? What do "HMAC" and "SHA1" mean? Ox5c5c and Ox3636 are probably octal numbers. Is this a computer problem and "HMAC" is the data in an accumulator? "SHA1" might be a shift operation on a computer register. In that case, I would expect "//" to be a binary operation, perhaps an "OR" operation.

Thank you for the attention. HMAC is a specific construction for calculating a message authentication code (MAC) involving a cryptographic hash function in combination with a secret cryptographic key.(wikipedia)

K is that key and a C is a counter that increments by one each time a message code is generated to ensure resulting codes are not the same.

Any cryptographic hash function, such as MD5 or SHA-1, may be used in the calculation of an HMAC; the resulting MAC algorithm is termed HMAC-MD5 or HMAC-SHA1 accordingly (wikipedia)

So I think were here dealing with HMAC-SHA1. The statement I'm trying to figure out appears in the beginning of this webpage: HOTP - Wikipedia, the free encyclopedia

The 0x... is a hex number. I was hoping there'd be some recognized interpretation of the symbols. || is often 'or' in computer code.