flag Mono

flag Mono

November 28, 2022
1 min read
flag-mono

flag Mono

Author
blueset
Category
Forensics
Points
368
Solves
47
Files
Assignment-broken.xps
Flag
SEKAI{OpenTypeMagicGSUBIsTuringComplete}

When writing the assignment, Miku used a font called flag Mono. Despite it looking just like a regular monospaced font, it claims itself to be stylistic in various ways.
”Perhaps there is something special about it”, Miku thought.

Note

This challenge shares the same file as Broken Converter.

If you inspect the font info in FontForge with Ctrl + Shift + F, you can see in the Lookup tab that four different “Style Sets” have been implemented into this font:

Inspecting the "Lookup" tab in FontForge

These are called “OpenType Stylistic Sets.” According to its official Microsoft documentation:

In addition to, or instead of, stylistic alternatives of individual glyphs […], some fonts may contain sets of stylistic variant glyphs corresponding to portions of the character set, e.g. multiple variants for lowercase letters in a Latin font.

In FontForge you can actually view the ruleset for these styles with the Edit Data button. This is the ruleset for ss01:

Inspecting stylistic set ruleset $2 in FontForge

ampersand quotesingle | a @<Single Substitution lookup 4> | g
| f @<Single Substitution lookup 4> | l a g
ampersand quotesingle parenleft | g @<Multiple Substitution lookup 5> |
ampersand | l @<Single Substitution lookup 4> | a g

Let’s test out typing flag on FontDrop! and changing the stylistic set:

Changing stylistic sets on FontDrop!