Friday, March 21, 2014

SIM cards tutorial Part 6: GSM Authentication Procedure



Whenever GSM mobile equipment (ME) is switched on, it has to be registered with operator’s network. For this registration, operator network should identify the user. There is a well-defined authentication procedure for verifying user identity of ME. The procedure is as follows.

  1. A GSM ME is switched ON. 
  2. ME uses a common channel to communicate with the operator network by providing IMSI. 
  3. When operator network detects an active unregistered ME, it verifies its IMSI. If it is a valid one, authentication procedure starts. Operator network will then fetch Ki corresponding to IMSI received from its database and will generate a random number (RAND). RAND is then encrypted with A3 algorithm with Ki as key to produce an output called SRES_1. Along with this, operator network will send this RAND to ME along with an indication of the algorithm used to generate SRES_1. 
  4. When ME receives RAND, it will pass this to SIM card along with the command RUN GSM ALGORITM. SIM card will encrypt this RAND with the same algorithm used by network operator using Ki in the SIM card as key and will generate SRES_2 as output. ME will send SRES_2 back to operator network. 
  5. On receiving SRES_2, operator network will match it with SRES_1 generated by it. If both matches authentication is success and ME is granted access to operator network

It is important to note that during authentication procedure, Ki is never transmitted anywhere. It always resides in operator network’s data base and in SIM card. Thus there is no way to get Ki for a third party.


Next part - SIM card Data Storage Architecture

3 comments:

Anonymous said...

oops

dilan said...

es in operator network’s data base and in SIM card. Thus there is no way to get Ki for a third party.

CODODO VIỆT NAM said...

ình huống này hơi quái… cho dù cô chỉ coi Lưu Tuấn Hàm là bạn bè, nhưng Lưu Tuấn Hàm có coi cô chỉ là bạn bè hay không thì rất khó nói. Hơn nữa còn không hề cố kỵ nói thích cô, đối với một người đã có đào tạo tiếng anh
trung tâm đào tạo tiếng anh
giày thể thao
cửa hàng giày thể thao
luyện thi toeic
tiếng anh cho người đi làm
tiếng anh cho người mới bắt đầu bạn trai, thực sự… Tuy cô tuyệt đối toàn tâm toàn ý với nam thần, nhưng lúc này, sao cô lại chợt thấy cảm giác tội lỗi vì đã “phản bội” nam thần vậy nè!

Post a Comment

Twitter Delicious Facebook Digg Stumbleupon Favorites More

 
Design by Free WordPress Themes | Bloggerized by Lasantha - Premium Blogger Themes | coupon codes