So, all of this sounds intimidating. Jailbreak, sign, secpack, unlock, baseband, iBoot, seczone, JailbreakMe, pwnage - there are lots of terms to learn, but most of them are defined here on the wiki. The basics:

Activation - to bypass the required iTunes signup.

Jailbreak - to allow full write and execute privileges on any Apple TV, iPad, iPhone or iPod touch.

Unlock - to allow the use of any mobile phone carrier's SIM.

Think of iPhone as a little computer, even though Apple doesn't want you to. It has a processor, RAM, a "hard drive", an operating system, and a cellular modem on the serial port.

Ways to learn about how jailbreaks work

(If you're more interested in learning how to develop for jailbroken devices, such as extensions/tweaks, check out the iPhoneDevWiki instead.)

The basic idea here is that there are lots of ways to learn more about jailbreaking, for people of all experience levels and backgrounds. You might want to learn enough to actually find vulnerabilities in iOS (which is a huge undertaking), or you might just enjoy learning a little bit out of curiosity. Go through this list and pick something that looks fun to read!

To learn a bit about what a jailbreak actually does to an iOS device, see this conversation with saurik - it explains the main technical changes that a typical jailbreak accomplishes. Here's also another conversation with saurik with a bit about the history of iOS jailbreaking and comparing it to Android rooting - "I often recommend that people who are interested in one day being able to hack something like iOS go spend some time cutting their teeth on simpler systems, such as Android".

Read winocm's recommendations for how to get started with iOS hacking: learning ARM, understanding low-level parts of iOS, reading open source code in iOS and OS X, learning programming, learning about security/fuzzing, and then learning iOS-specific tools and tricks. She's also written a bunch of other posts about iOS security research.

Read iOS Hacker's Handbook, published in May 2012: "The award-winning author team, experts in Mac and iOS security, examines the vulnerabilities and the internals of iOS to show how attacks can be mitigated. The book explains how the operating system works, its overall security architecture, and the security risks associated with it, as well as exploits, rootkits, and other payloads developed for it."

Listen to the 25C3 presentation "Hacking the iPhone". This was in 2008, but it explains the basics in detail.

See the presentation "Strategic Analysis of the iOS Jailbreaking Development Community" by Dino Dai Zovi in November 2012.

Members of the team that built Corona for iOS 5.0.1 gave presentations about it, and there are PDFs of their slides available here: Corona for A4 and Corona/Absinthe for A5.

Play with Damn Vulnerable iOS Application (DVIA), "a platform to mobile security enthusiasts/professionals or students to test their iOS penetration testing skills in a legal environment".

Study the available open source jailbreaking tools.

Read fuzzing for some explanation of how that technique has been used on iOS, and read how to reverse for some inspiration.

If you want to really get started, learn assembler for ARM processors. Open Security Training has "Introduction to ARM" materials, for example.

Jonathan Levin posts interesting iOS reverse engineering research. His series of books on "*OS Internals" are a definitive reference. In particular, Volume III deals exclusively with security, insecurity, and dissects every modern jailbreak from evasi0n (6.0) through async_wake (11.1.2) in detail.

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