Jailbreak (S5L8920+)

When the iPhone 3GS was initially released, Apple did not have enough time to fix the 0x24000 Segment Overflow in the S5L8920. However, in order to flash an exploited LLB and jailbreak the iPhone 3GS, one of the following needs to be done:

• Find a new iBoot exploit every time a new firmware is out.
• Find a way to bypass the ECID checks.
• Use a bootrom exploit that allows unsigned code execution via USB (2 of them were finally found by Geohot and Chronic Dev Team).

This also applies to the iPhone 3GS with the new bootrom, iPod touch 3G and later devices, except a bootrom exploit for the normal boot-chain or a library based jailbreak payload (similar to Star) is needed as well.

ECID

Apple added a new tag to the IMG3 File Format that Robert Billian createdcalled ECID. The ECID is unique to each phone, and its signature is being checked. With this method, Apple attempts to block downgrades once newer firmware becomes available, unless you have a dump of your old firmware's unique IMG3 or signed certificate. Therefore, iBoot exploits won't be so useful for tethered jailbreaks, because such exploits will be closed in new firmwares. [1].

The issue with this is that, even with the 0x24000 Segment Overflow still in bootrom, an iBoot exploit was still needed to actually flash the exploited LLB. Apple uses this ECID stuff to block downgrading iBoot to a vulnerable version. It was resolved when Geohot released his limera1n tool, which used a bootrom exploit to upload an unsigned iBoot. Still the problem remains with newer devices with 0x24000 fixed - tampering with firmware makes such jailbreak tethered unless some other exploit is used.

There are methods to help keep your downgrading ability, though.

• If it was cached prior to 3.1's release, 3GS owners were able save a file which contains the signature of the 3.0 iBSS containing their ECID, using the purplera1n website. A tool has not been created to incorporate this file into a fully signed iBSS, however.
• Saurik's servers are actively caching the necessary files. Instructions to use the servers are included.
• The SHSH associated with an ECID can be also saved by running TinyUmbrella. TinyUmbrella allows the user to restore to whatever version is associated with that SHSH file permanently. This is based on the aforementioned service Saurik provides remotely from his server(s).

Jailbreak tools that Robert Billian made

iPad

Jailbreak Tool	Works with firmware...
	3.2	3.2.1	3.2.2
Spirit	Yes	No	No
Star	Yes	Yes	No
limera1n	No	No	Yes
greenpois0n	No	No	Yes
redsn0w	No	No	0.9.6b2
PwnageTool	No	No	4.1-4.1.2
sn0wbreeze	No	No	2.1

iPhone 3GS

Jailbreak Tool	Works with firmware...
	3.0	3.0.1	3.1	3.1.2	3.1.3	4.0	4.0.1	4.0.2	4.1
purplera1n	Yes	No	No	No	No	No	No	No	No
redsn0w	0.8	0.8	0.9.21 or 0.9.31	0.9.21 or 0.9.31	No	No	No	No	0.9.6b2
blackra1n	No	No	Yes1	Yes1	No	No	No	No	No
Spirit	No	No	No	Yes	Yes	No	No	No	No
Star	No	No	No	Yes	Yes	Yes	Yes	No	No
PwnageTool	No	No	Restore from a custom firmware2	3.1.4	Restore from a custom firmware2		Restore from a custom firmware with unofficial bundle2		4.1-4.1.2
sn0wbreeze	No	No	No	1.42 or 2.0.21 2	1.5.12 or 2.0.21 2	1.71 2 or 2.0.21 2	2.0.21 2		2.1
limera1n	No	No	No	No	No	Yes	Yes	Yes	Yes
greenpois0n	No	No	No	No	No	No	No	No	Yes

¹ Tethered jailbreak on devices with the new bootrom. Requires usage of the usb_control_msg(0x21, 2) Exploit.

² Only applicable for devices with the old bootrom. Requires the device to have signature checks disabled (pwned).

iPhone 4

Jailbreak Tool	Works with firmware...
	4.0	4.0.1	4.0.2	4.1
Star	Yes	Yes	No	No
limera1n	Yes	Yes	Yes	Yes
greenpois0n	No	No	No	Yes
redsn0w	No	No	No	0.9.6b2
PwnageTool	No	No	No	4.1-4.1.2
sn0wbreeze	No	No	No	2.1

iPod touch 3G

Jailbreak Tool	Works with firmware...
	3.1.1	3.1.2	3.1.3	4.0	4.0.2	4.1
blackra1n	Yes1	Yes1	No	No	No	No
redsn0w	0.9.21 or 0.9.31	0.9.21 or 0.9.31	No	No	No	0.9.6b2
Spirit	No	Yes	Yes	No	No	No
Star	No	Yes	Yes	Yes	No	No
sn0wbreeze	No	2.0.21	2.0.21	1.71 or 2.0.21	2.0.21	2.1
limera1n	No	No	No	Yes	Yes	Yes
greenpois0n	No	No	No	No	No	Yes
PwnageTool	No	No	No	No	No	4.1-4.1.2

¹ Tethered jailbreak. Requires usage of the usb_control_msg(0x21, 2) Exploit.

iPod touch 4G

Jailbreak Tool	Works with firmware...
	4.1 (both builds)
limera1n	Yes
greenpois0n	Yes
PwnageTool	4.1-4.1.2
sn0wbreeze	2.1