A B Verschlsselung schtzt nur Inhalte, nicht die Metadaten! Wer - - PowerPoint PPT Presentation

Anonymität? Ünüberwachbare Kommunikation!

A B

Verschlüsselung schützt nur Inhalte, nicht die Metadaten!

• Wer mit wem?
• Wann?
• Was?

1-hop proxy (VPN, SSH Tunnel etc)

Bob2 Bob1 Bob3 Alice2 Alice1 Alice3 Relay “Y” “ Z ” “X”

Problem Vertrauenswürdigkeit und einfache Überwachbarkeit

Bob2 Bob1 Bob3 Alice2 Alice1 Alice3 Evil Relay?

Coerced Relay? Monitored Relay?

“Y” “ Z ” “X”

Tor

Tor

Bob Alice R1 R2 R3 R4 R5

Tor

Bob Alice R1 R2 R3 R4 R5

Tor

Bob Alice R1 R2 R3 R4 R5

Tor

Bob Alice R1 R2 R3 R4 R5 Bob2

Problem: (sufficiently) global passive adversaries

Bob Alice R1 R2 R3 R4 R5

• “Not secure against end-to-end attacks:

Tor does not claim to completely solve end-to-end timing or intersection attacks.“ (Tor Design Paper, 2004)

• A global passive adversary is the most

commonly assumed threat when analyzing theoretical anonymity

• designs. But like all practical low-

latency systems, Tor does not protect against such a strong adversary.“ (ebd.)

“The results show that Tor faces even greater risks from traffic correlation than previous studies suggested. An adversary that provides no more bandwidth than some volunteers do today can deanonymize any given user within three months of regular Tor use with over 50% probability and within six months with over 80% probability.” (Users get routed: Traffic Correlation on Tor by Realistic Adversaries, 2013)

Alternative: Broadcast-Architektur

Bob2 Bob1 Bob3 Alice2 Alice1 Alice3 E(Bob2, “Z”) E(Bob2, “Z”) E(Bob2, “Z”)

Beispiel Bitmessage

Alternative: Mixnets

Bob Alice R1 R2 R3 (R4) (R5)

Tor: Verbindungsaufbau

Bob Alice R1 R2 R3 (R4) (R5)

Tor: Verbindungsaufbau

Bob Alice R1 R2 R3 (R4) (R5)

Tor: Verbindungsaufbau

Bob Alice R1 R2 R3 (R4) (R5)

Tor: Verbindungsaufbau

Bob Alice R1 R2 R3 (R4) (R5)

Mixnets: nachrichtenbasiert statt paketbasiert !

Bob Alice R1 R2 R3 (R4) (R5)

Bob Alice R1 R2 R3 (R4) (R5)

Bob Alice R1 R2 R3 (R4) (R5)

Bob Alice R1 R2 R3 (R4) (R5)

Bob Alice R1 R2 R3 (R4) (R5)

Bob Alice R1 R2 R3 (R4) (R5)

Bob Alice R1 R2 R3 (R4) (R5)

Bob Alice R1 R2 R3 (R4) (R5)

Mix-Strategien

• Pool/Batching Mix

– sammle x Nachrichten (“threshold mix”) – warte x Minuten (“timed mix”)

(Mixmaster: timed + threshold: nur wenn x Nachrichten eingangen sind wird Queue nach Timeout geleert/versendet)

• Stop & Go Mixes: Delay der einzelnen Hops

vom Nutzer vorgegeben

• 1

9 7 8 L i mi t a t i

• n

s

• f

E n d

• t
• E

n d E n c r y p t i

• n

i n S e c u r e C

• mp

u t e r N e t w

• r

k s ( K a r g e r )

• 1

9 8 1 U n t r a c e a b l e e l e c t r

• n

i c ma i l , r e t u r n a d d r e s s e s a n d d i g i t a l p s e u d

• n

y ms ( D a v i d C h a u m)

• 1

9 8 5 N e t w

• r

k s Wi t h

• u

t U s e r O b s e r v a b i l i t y – D e s i g n O p t i

• n

s ( P f i t z ma n n )

• 1

9 9 1 I S D N

• M

i x e s ( P f i t z ma n n )

• [

1 9 9 5 “ I n i t i a l w

• r

k

• n

O n i

• n

R

• u

t i n g b e g i n s ” ]

• 1

9 9 8 R e a l

• T

i me M I X e s ( P f i t z ma n n ) h t t p : / / f r e e h a v e n . n e t / a n

• n

b i b

• 1

9 9 2 a n

• n

. p e n e t . f i ( T y p R e ma i l e r )

( 5 , N u t z e r , 8 N a c h r i c h t e n / T a g , ~ $ 1 / M

• n

a t )

1

1 9 9 5 : C h u r c h

• f

S c i e n t

• l
• g

y , L

• s

A n g e l e s F B I F i n n l a n d → →

• 1

9 9 2 C y p h e r p u n k s

• R

e ma i l e r ( T y p 1 R e ma i l e r )

E i n f a c h e r R e ma i l e r , k e i n M i x i n g ( t i mi n g a n a l y s i s ) , k e i n P a d d i n g ( t r a f f i c → → a n a l y s i s )

• 1

9 9 4 M i x ma s t e r ( T y p 2 )

• 1

9 9 5 a n

• n

y mi z e r , c 2 . n e t n y ms e r v e r

• 2

2 M i x mi n i

• n

( T y p 3 )

• [

2 4 T

• r

D e s i g n P a p e r ]

1

h t t p : / / f r e e h a v e n . n e t / a n

• n

b i b / c a c h e / r e ma i l e r

• h

i s t

• r

y . h t ml

Probleme Mixnets

• Historisch:

– Keine Zustellungsgarantie – Lange Nachrichtenlaufzeiten (Tage!) – Komplizierte UIs, fehlende Integration – Spam-/Abuse-Problematik

• Loopix Anonymity System (März 2017)

– Stop & Go – aktive Angriffe erkennen durch “loops” – “message latency in the order of seconds”

Katzenpost

• “echtes” Open Source Projekt

– Spezifikation auf Github – Implementierung in Go – [ Integration in K9 Mail ] – Finanzierung durch EU!

https://katzenpost.mixnetworks.org/