Aphasia

Description

In this challenge, you will need to extract the flag from the secure records, but how?

http://memenc.challenges.bsidestlv.com/help

Solution

We access the help API and get the following definitions:

Let's try the APIs out.

We start with the "get details" API:

Let's try to read from the first record:

We can read from this record, marked as "Non-Secure", using this API.

What does the hash API give us? We read the hash of 1 byte of data from record 0, offsets 0, 1, and 2.

These are the SHA256 values for 8e, c1 and 62 respectively:

So we can use the "hash" API to deduce the contents of a non-secure record, giving us what we read using the "read" API.

Now let's go find a secure record and try the same trick:

Looks like this works for secure record as well.

Using the following script, we can extract all the secure records:

Running it, we get:

One value seems to repeat itself many times, what does it represent?