As a programming exercise I need to decrypt a message. The only clues that I have is that it seems are:

The encoded message contains only Base64 Characters
a n letter sequence (n in 1,4,7,10) times it returns an encrypted message with "==".
a n letter sequence (n in 2,5,8,11) times it returns an encrypted message with "=".
a n letter sequence (n in 3,6,9,12) returns an encrypted message without a specific character.

I do not want a solution, I am just wondering if this sequence of occurrences for the equal sign provide a clue or not.

The = signs relate to the length of the string being encoded in Base64. Essentially, in probably the most common form of Base64, = is used as a padding character to ensure that the last block can be decoded properly.

Base64 is not encryption - there is no hiding going on in it - but is often used to allow for binary data to be sent in text only form. All the characters used in Base64 will paste correctly, and can be entered using a keyboard with no modifier keys beyond shift.
