NOTE:
Though the body is identical to I am both lock and key - who am I?, a different answer is expected, and thus this is not a duplicate.
Cyrnfr qb abg pybfr guvf dhrfgvba.
Thanks!
Enter! Small or large, as the case may be
I'll assist you - it's easy! - I'm both lock and key
Who am I?
HINTS:
1
Gur nafjre vf bs yratgu svir
2
Weet bksa, co vhyudt, mu qhu qbb cqhhyut, unsufj oek qdt jxqj tkbb rhejxuh mxe xqhtbo sxqdwui qj qbb!
All in all, @Shahriar and @rhsquared, had it all. I just joined their answer and added an explanation for hints.
I think the answer is
ROT13
Enter! Small or large, as the case may be
ROT13 can work on both "small" and "large" case
I'll assist you - it's easy! - I'm both lock and key
ROT13 is both lock and key in the sense that a text "encrypted" with ROT13 can be decrypted by applying a new ROT13 operation.
Hint 1
ROT13 has 5 characters
Hint 2
"Good luck, my friend, we are all married, except you and that dull brother who hardly changes at all!" All ROTxx is "maried" with ROT[26-xx] except for ROT13 married with himself, and ROT0, who doesn't change the text at all.
The answer is-
ROT13
Because-
It's both the encryption method and decryption method for hiding plaintext.
Considering that you used:
both Rot13 and Rot10 in you puzzle and hints I would say the answer is Rot16 in order to match the requirement for 5 letter length.
Enter! Small or large, as the case may be
The Rotxx encryption works on both caps (large) and small letters.
I'll assist you - it's easy! - I'm both lock and key
With the ROT encryption/decryption you can both encode and decode the text. We only need to keep in mind that only Rot13 is 'symetrical'. In all the rest the lock/key pair the sum of the Rotxx + Rotyy is 26. Considering that Hint 2 can be decoded using Rot10, I think the answer is its missing counterpart Rot16.
