Challenge 15: Base64 Encoding

Difficulty: Easy
Category: Non-Printable Ratio Bypass

Objective

Hide binary/non-printable content in a file while keeping the non-printable byte ratio at exactly 0%. The file must still be usable — the original binary data should be recoverable at runtime.

Scanner Behavior

The scanner calculates the ratio of non-printable bytes to total bytes for any file that is 64 bytes or larger. A byte is considered “non-printable” if it falls outside the standard printable ASCII range (0x20–0x7E, plus common whitespace like tabs and newlines).

If more than 40% of the file’s bytes are non-printable, the scanner flags the file as suspicious.

The scanner performs this check on the raw file contents as stored on disk. It does not execute or interpret the file in any way.

Rules

Your file must contain data that, when decoded, produces arbitrary binary content (including non-printable bytes).
The raw file on disk must have a non-printable byte ratio of 0%.
The file must be at least 64 bytes in size.
You must demonstrate that the original binary data is recoverable.

Hints

There’s a very common encoding that turns any binary data into printable ASCII characters.
It’s used in email attachments daily.
The scanner only sees what’s on disk — it doesn’t understand what the text represents.

View Solution