Reverse-engineering Instagram to access the private API

http://definedcodehosting.com/reverse.html

by 1il7890 • 13 years ago

59 15 13 years ago

potomak• 13 years ago

Note that Instagram doesn't encrypt requests to their private API, they're only signing them. In fact the parameter is called 'signed_body', not 'encrypted_body'.

Anyway interesting post.

CGamesPlay3• 13 years ago

The traffic is encrypted over SSL (HTTPS), so there's no need for double-encryption, since presumably the app can trust the DNS and certificate chains on the device. If I were a paranoid Instagram developer, though, I could even use a custom certificate chain that only trusted certificates on my server, so there's no point to doing the encryption in the app.

SifJar• 13 years ago

Interesting write up. Seems rather simple, really. Presumably Instagram could change their private key and rollout a new client version on each platform, breaking all third party apps using the current key though. Although I guess it'd be just as easy to get it again.

Zariel• 13 years ago

Well if you have the private key on the device you can always pull it out, so really they should have used public key encryption if they didn't want people to forge the signatures.

CGamesPlay3• 13 years ago

Public key encryption to sign involves encrypting using my own private key. Which would be on the phone, and so any end user could pull it from the device.

sjtgraham• 13 years ago

Is it still the case that the app only uses HTTPS to create a session and plain HTTP for everything else? I remember that was the case about a year ago after using mitmproxy to sniff traffic, although I don't recall HMAC being used to sign requests then. Anyway, I wondered then why nobody had used firesheep to devastating effect, e.g. a bot sitting on an open wifi and posting NSFW images to any account on the network.

xuki• 13 years ago

I'm fairly certain they use HTTPS for all the requests involve user token.

rnaud• 13 years ago

Isn't the fact that they are using a simple HMAC-SHA256 hash also a root of the problem?

If instead of using the POST data only to create the hash they added another information, like a the hour of the day. Wouldn't it be way harder for a hacker to actually understand what went into signing the request?

meritt• 13 years ago

Not really. He decompiled the code so it's pretty simple to figure out regardless.

Reverse-engineering Instagram to access the private API

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