The most common and most likely answer to this crossword clue is the 7 letter word KEYWORD
I've seen this crossword clue in The Guardian
K
E
Y
W
O
R
D
Buddy explains!

The straight part
We know that "access to cipher" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case access to cipher = keyword.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does KEYWORD mean?
KEYWORD noun- Any word used as the key to a code.
- Any word used in a reference work to link to other words or other information.
- A reserved word used to identify a specific command, function etc.
- Any word that occurs in a text more often than normal.
- To tag with keywords, as for example to facilitate searching.