# What's the Apostrophe or single quote of a variable means in cryptography?

What's the meaning of Apostrophe over a variable in the context conversations of verification?

Reference number: https://people.eecs.berkeley.edu/~jfc/'mender/IEEESP02.pdf

• Err, what specialty are you expecting then the obvious; two conversations that share $C_a$ and $C_b$ and rest are different ( not necessarily). Feb 27, 2022 at 19:39
• It's not just cryptography; it's common mathematical and scientific notation. See wikipedia and wolfram. Note it's straight, where close-quote and apostrophe are curved in proper typesetting and (even?) Unicode, though ASCII combines them. Feb 27, 2022 at 23:42

In the context you asked about, we are talking about an exchange that involves six variables. We overhear two separate exchanges with the same protocol, one exchange where we call the six variables $$C_a, C_b, c, v, z_a, z_b$$; the other exchange which involve the same $$C_a, C_b$$ identifiers, but the other four may be different. The authors could have decided to call the variables involved with different identifiers, say, $$d, u, w_a, w_b$$; however that would have been confusing, because it wouldn't be obvious that $$c$$ and $$d$$ are in the same logical position in the two exchanges.
Instead, he gave the values in the second exchange related names, $$c', v', z'_a, z'_b$$; that way, it is clear that, while $$c$$ and $$c'$$ are different, they both come from the same place in the respective exchange.