Roof of Africa

The brief

They say Africa's highest peak holds ancient secrets in its frozen glaciers. A photograph has been intercepted, but its true meaning is locked away, protected by the mountain's most famous number. Can you reach the summit and uncover what lies hidden?

• roof_of_africa.jpg, 610 KB

In short

A JPEG carried a steghide payload locked by a passphrase. The brief pointed to the mountain's most famous number, and Kilimanjaro's height of 5,895 metres opened it.

One photo, nothing on the surface

The file is a single JPEG, 1600 by 1056 pixels. Its metadata says nothing, there is no comment, and no data sits after the image ends.

Room for 31.4 KB inside

Steghide hides data in a JPEG's compressed coefficients and locks it with a passphrase. A quick look showed room for 31.4 KB, and an empty passphrase opened nothing. The key had to come from the text.

The mountain's most famous number

Africa's highest peak is Kilimanjaro, and the number everyone knows is its height. The lab wrote 24 candidates around it, 5,895 metres, 19,341 feet, nearby values and names.

5895 opens it, 30 seconds in

5895 matched, confirmed by the payload's own checksum. Extracting with it gave a small text file, roof_flag_v2.txt, with the flag inside. The whole solve took 30 seconds.

The insight

A hidden payload is only as strong as its passphrase, and a famous public number hinted in the brief fits on a list of 24 guesses.

The flag

hiCTF{h4kun4_m4t4t4_m34ns_n0_w0rr13s}