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Defeating IMSI catchers
CCS 2015 10-13-2015 Denver
Fabian van den Broek, Roel Verdult and Joeri de Ruiter
IMSI catching
For this talk: IMSI catching == catching IMSIs (and nothing else)
Defeating IMSI catchers CCS 2015 10-13-2015 Denver Fabian van den - - PowerPoint PPT Presentation
Defeating IMSI catchers CCS 2015 10-13-2015 Denver Fabian van den - - PowerPoint PPT Presentation
Defeating IMSI catchers CCS 2015 10-13-2015 Denver Fabian van den Broek, Roel Verdult and Joeri de Ruiter IMSI catching For this talk: IMSI catching == catching IMSIs (and nothing else) IMSI catching For this talk: IMSI catching ==
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IMSI catching
For this talk: IMSI catching == catching IMSIs (and nothing else) IMSI catching is an attack that works on all generations of mobile networks
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So, what is an IMSI?
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So, what is an IMSI?
- IMSI = International Mobile Subscriber Identity
- unique identifier of a SIM
- IMEI = IMSI = phone number
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So, what is an IMSI? (II)
15 digits that identify:
- home country
- home network
- user
Example IMSI:
310030123456789
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So, what is an IMSI? (II)
15 digits that identify:
- home country
- home network
- user
Example IMSI:
310030123456789
- The United States
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So, what is an IMSI? (II)
15 digits that identify:
- home country
- home network
- user
Example IMSI:
310030123456789
- The United States
- AT&T
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So, what is an IMSI? (II)
15 digits that identify:
- home country
- home network
- user
Example IMSI:
310030123456789
- The United States
- AT&T
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And the IMSI is broadcasted in plain text!
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IMSI catchers
- passive
- active
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IMSI catchers
- passive
- active
- eavesdropping and insertion
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IMSI catchers
- passive
- active
- eavesdropping and insertion
- expensive and exclusively sold to governments
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IMSI catchers
- passive
- active
- eavesdropping and insertion
- expensive and exclusively sold to governments
- r home made for $100,-
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Why catch IMSIs?
- IMSIs reveal information
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Why catch IMSIs?
- IMSIs reveal information
- Attack location privacy
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Why catch IMSIs?
- IMSIs reveal information
- Attack location privacy
– Tracking
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Why catch IMSIs?
- IMSIs reveal information
- Attack location privacy
– Tracking – Location monitoring
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Why catch IMSIs?
- IMSIs reveal information
- Attack location privacy
– Tracking – Location monitoring
- Linking identities to devices
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Why catch IMSIs?
- IMSIs reveal information
- Attack location privacy
– Tracking – Location monitoring
- Linking identities to devices
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Why catch IMSIs?
- IMSIs reveal information
- Attack location privacy
– Tracking – Location monitoring
- Linking identities to devices
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Why catch IMSIs?
- IMSIs reveal information
- Attack location privacy
– Tracking – Location monitoring
- Linking identities to devices
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3G+4G authentication (simplified)
SIM IMSI, K, SQN Serving network Home network IMSI → Ki, SQNi identity request identity response (IMSI) IMSI
1
RAND, AUTN, XRES, CK authentication request (RAND, AUTN)
2 3
authentication response (SRES) verify SRES = XRES encrypted using CK Location Update(IMSI)
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Who is to blame?
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Who is to blame?
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Who is to blame?
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Our solution
- uses temporary pseudonyms: PMSIs
- can be deployed by any Home network / provider
- does not prevent IMSI catching, but hinders attack goals (e.g.
tracking, etc.)
- is formally verified using ProVerif
- successor PMSIs are only known to SIM and Home network
- the Home network generates successor PMSIs
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Our solution
- uses temporary pseudonyms: PMSIs
- can be deployed by any Home network / provider
- does not prevent IMSI catching, but hinders attack goals (e.g.
tracking, etc.)
- is formally verified using ProVerif
- successor PMSIs are only known to SIM and Home network
- the Home network generates successor PMSIs,
but how to get them to the SIM?
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3G+4G solution
SIM P, P′, κ, K, SQN Serving network Home network PMSI → P, P′, κi, Ki, SQNi identity request P ← P′ identity response (P) P
1
RAND, AUTN, XRES, CK authentication request (RAND, AUTN)
2
3
authentication response (SRES) verify SRES = XRES encrypted using CK Location Update(P)
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3G+4G solution