re: what’s up johnny? - def con con 27/def con 27... · s/mime pgp s/mime pgp windows thunderbird...
TRANSCRIPT
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Re: What’s up Johnny?Covert Content Attacks on Email End -To-End Encryption
Jens Müller, Marcus Brinkmann, Damian Poddebniak,Sebastian Schinzel, Jörg Schwenk
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Remember EFAIL?
2
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• Last year: EFAIL
Remember EFAIL?
2
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• Last year: EFAIL– Major attack with a logo
Remember EFAIL?
2
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• Last year: EFAIL– Major attack with a logo
– Novel attack techniques
targeting S/MIME + PGP
Remember EFAIL?
2
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• Last year: EFAIL– Major attack with a logo
– Novel attack techniques
targeting S/MIME + PGP
• Today: non-crypto attacks
Remember EFAIL?
2
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• Last year: EFAIL– Major attack with a logo
– Novel attack techniques
targeting S/MIME + PGP
• Today: non-crypto attacks– Targeting encryption and digital signatures
Remember EFAIL?
2
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1. Introduction2. Attacks on Encryption3. Attacks on Signatures4. Evaluation5. Mitigation
Overview
3
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1. Introduction2. Attacks on Encryption3. Attacks on Signatures4. Evaluation5. Mitigation
Overview
3
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Technology's promise
4
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I. “Strong crypto is virtually unbreakable.”
Technology's promise
4
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I. “Strong crypto is virtually unbreakable.”II. “Digital signature will prevail. Math wins.”
Technology's promise
4
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I. “Strong crypto is virtually unbreakable.”II. “Digital signature will prevail. Math wins.”
Technology's promise
…claims I. and II. could be bypassed witha single reply to a benign looking email?
What if…
4
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From: [email protected]: [email protected]: Important news
Some ASCII text message…
Traditional RFC822 email
5
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From: [email protected]: [email protected]: Important news
Some ASCII text message…
Traditional RFC822 email
5
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From: [email protected]: [email protected]: Important news
Some ASCII text message…
Traditional RFC822 email
5
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From: [email protected]: [email protected]: Important news
-----BEGIN PGP MESSAGE-----…-----END PGP MESSAGE-----
Traditional PGP/Inline
6
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From: [email protected]: [email protected]: Important news
-----BEGIN PGP MESSAGE-----…-----END PGP MESSAGE-----
Traditional PGP/Inline
6
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From: [email protected]: [email protected]: Important news
-----BEGIN PGP MESSAGE-----…-----END PGP MESSAGE-----
Traditional PGP/Inline
6
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Multipart MIME email
7
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Content-type: text/plain
Some ASCII text message…
Content-type: text/plain
This is the 2nd part
From: [email protected]: [email protected]: multipart/mixed; boundary="XXX"
--XXX
--XXX
--XXX--
Multipart MIME email
7
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Content-type: text/plain
Some ASCII text message…
Content-type: text/plain
This is the 2nd part
From: [email protected]: [email protected]: multipart/mixed; boundary="XXX"
--XXX
--XXX
--XXX--
Multipart MIME email
7
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Content-type: text/plain
Some ASCII text message…
Content-type: text/plain
This is the 2nd part
From: [email protected]: [email protected]: multipart/mixed; boundary="XXX"
--XXX
--XXX
--XXX--
Multipart MIME email
7
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Content-type: text/plain
Some ASCII text message…
Content-type: text/plain
This is the 2nd part
From: [email protected]: [email protected]: multipart/mixed; boundary="XXX"
--XXX
--XXX
--XXX--
Multipart MIME email
7
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Content-type: text/plain
Some ASCII text message…
Content-type: text/plain
This is the 2nd part
From: [email protected]: [email protected]: multipart/mixed; boundary="XXX"
--XXX
--XXX
--XXX--
Multipart MIME email
multipart/mixed
7
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Content-type: text/plain
Some ASCII text message…
Content-type: text/plain
This is the 2nd part
From: [email protected]: [email protected]: multipart/mixed; boundary="XXX"
--XXX
--XXX
--XXX--
Multipart MIME email
multipart/mixed
texttext
7
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From: [email protected]: [email protected]: multipart/mixed; boundary="XXX"
--XXX
--XXX
--XXX--
Content-type: text/html
<b>HTML</b> message…
Content-type: application/pdf
%PDF-1.4 […]
Multipart MIME email
multipart/mixed
pdfhtml
7
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From: [email protected]: [email protected]: Important newsContent-Type: application/pkcs7-mime
MIAGCSqGSIb3DQEHA6CAMIACAQAxggHJMIIB…
S/MIME
8
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From: [email protected]: [email protected]: Important newsContent-Type: application/pkcs7-mime
MIAGCSqGSIb3DQEHA6CAMIACAQAxggHJMIIB…
S/MIME
8
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From: [email protected]: [email protected]: Important newsContent-Type: application/pkcs7-mime
MIAGCSqGSIb3DQEHA6CAMIACAQAxggHJMIIB…
S/MIME
8
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OpenPGP (RFC 4880)• Favored by privacy advocates• Web-of-trust (no authorities)
S/MIME (RFC 5751)• Favored by organizations• Multi-root trust-hierarchies
Two competing standards
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OpenPGP (RFC 4880)• Favored by privacy advocates• Web-of-trust (no authorities)
S/MIME (RFC 5751)• Favored by organizations• Multi-root trust-hierarchies
Two competing standards
9
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1. Introduction2. Attacks on Encryption3. Attacks on Signatures4. Evaluation5. Mitigation
Overview
10
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1. Introduction2. Attacks on Encryption3. Attacks on Signatures4. Evaluation5. Mitigation
Overview
10
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Attacker model
11
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• Eve has captured ciphertext
Attacker model
11
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• Eve has captured ciphertext• Can modify email structure
Attacker model
11
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• Eve has captured ciphertext• Can modify email structure • Can re-send it to the victim
Attacker model
11
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• Eve has captured ciphertext• Can modify email structure • Can re-send it to the victim
– Either to recipient or sender
Attacker model
11
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• Eve has captured ciphertext• Can modify email structure • Can re-send it to the victim
– Either to recipient or sender– Both can decrypt the email
Attacker model
11
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Covert content attack: Decryption oracle
12
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Covert content attack: Decryption oracle
12
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Covert content attack: Decryption oracle
12
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Covert content attack: Decryption oracle
12
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Decryption oracle
From: [email protected]
Content-Type: application/pkcs7-mime
MIAGCSqGSIb3DQEHA6CAMIACAQAxggHJMIIB…
13
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Decryption oracle
From: [email protected]
Content-Type: application/pkcs7-mime
MIAGCSqGSIb3DQEHA6CAMIACAQAxggHJMIIB…
13
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Decryption oracle
From: [email protected]
Content-Type: application/pkcs7-mime
MIAGCSqGSIb3DQEHA6CAMIACAQAxggHJMIIB…
13
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Decryption oracle
From: [email protected]
Content-Type: application/pkcs7-mime
MIAGCSqGSIb3DQEHA6CAMIACAQAxggHJMIIB…
13
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Decryption oracle
From: [email protected]
Content-Type: application/pkcs7-mime
MIAGCSqGSIb3DQEHA6CAMIACAQAxggHJMIIB…
13
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Content-type: multipart/mixed; boundary="XXX"
--XXX
--XXX
--XXX--
Decryption oracle
From: [email protected]
Content-Type: application/pkcs7-mime
MIAGCSqGSIb3DQEHA6CAMIACAQAxggHJMIIB…
13
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Content-type: multipart/mixed; boundary="XXX"
--XXX
--XXX
--XXX--
Decryption oracle
From: [email protected]
Content-Type: application/pkcs7-mime
MIAGCSqGSIb3DQEHA6CAMIACAQAxggHJMIIB…
Content-type: text/plain
What's up Johnny?
13
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Content-type: multipart/mixed; boundary="XXX"
--XXX
--XXX
--XXX--
Decryption oracle
From: [email protected]
Content-Type: application/pkcs7-mime
MIAGCSqGSIb3DQEHA6CAMIACAQAxggHJMIIB…
Content-type: text/plain
What's up Johnny?
multipart/mixed
???text
13
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Content-type: multipart/mixed; boundary="XXX"
--XXX
--XXX
--XXX--
Content-type: text/plain
Secret message, for Johnny's eyes only…
Decryption oracle
From: [email protected]
Content-type: text/plain
What's up Johnny?
multipart/mixed
text secret
13
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Content-type: multipart/mixed; boundary="XXX"
--XXX
--XXX
--XXX--
Content-type: text/plain
Secret message, for Johnny's eyes only…
Decryption oracle
From: [email protected]
Content-type: text/plain
What's up Johnny?
13
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Content-type: multipart/mixed; boundary="XXX"
--XXX
--XXX
--XXX--
Content-type: text/plain
Secret message, for Johnny's eyes only…
Decryption oracle
From: [email protected]
Content-type: text/plain
What's up Johnny?
13
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Content-type: multipart/mixed; boundary="XXX"
--XXX
--XXX
--XXX--
Content-type: text/plain
Secret message, for Johnny's eyes only…
Decryption oracle
From: [email protected]
Content-type: text/plain
What's up Johnny?\n\n\n\n\n\n…
13
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Content-type: multipart/mixed; boundary="XXX"
--XXX
--XXX
--XXX--
Content-type: text/plain
Secret message, for Johnny's eyes only…
Decryption oracle
From: [email protected]
Content-type: text/plain
What's up Johnny?\n\n\n\n\n\n…
13
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Content-type: multipart/mixed; boundary="XXX"
--XXX
--XXX
--XXX--
Content-type: text/plain
Secret message, for Johnny's eyes only…
Decryption oracle
From: [email protected]
Content-type: text/html
What's up Johnny? <!--
13
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Content-type: multipart/mixed; boundary="XXX"
--XXX
--XXX
--XXX--
Content-type: text/plain
Secret message, for Johnny's eyes only…
Decryption oracle
From: [email protected]
Content-type: text/html
What's up Johnny? <!--
13
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Content-type: multipart/mixed; boundary="XXX"
--XXX
--XXX
--XXX--
Content-ID: <part2>
Secret message, for Johnny's eyes only…
Decryption oracle
From: [email protected]
Content-type: text/html
What's up Johnny? <img src="cid:part2">
13
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Content-type: multipart/mixed; boundary="XXX"
--XXX
--XXX
--XXX--
Content-Disposition: attachment
Secret message, for Johnny's eyes only…
Decryption oracle
From: [email protected]
Content-type: text/plain
What's up Johnny?
13
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1. Introduction2. Attacks on Encryption3. Attacks on Signatures4. Evaluation5. Mitigation
Overview
14
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1. Introduction2. Attacks on Encryption3. Attacks on Signatures4. Evaluation5. Mitigation
Overview
14
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Covert content attack: Signing oracle
15
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Covert content attack: Signing oracle
15
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Covert content attack: Signing oracle
15
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Covert content attack: Signing oracle
15
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Covert content attack: Signing oracle
15
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From: [email protected]: [email protected]: text/html
What's up Johnny?I hereby declare war.
Signature oracle
16
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Signature oracle
From: [email protected]: [email protected]: text/html
What's up Johnny?<div class="covert"> I hereby declare war. </div>
16
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Signature oracle
From: [email protected]: [email protected]: text/html
<style>IF condition:Hide * but show .covert
</style>What's up Johnny?<div class="covert">I hereby declare war.</div>
16
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Signature oracle
From: [email protected]: [email protected]: text/html
<style>@media (max-device-width: 834px) {.covert {visibility: hidden;}}
</style>What's up Johnny?<div class="covert">I hereby declare war.</div>
hide covertcontent on mobile devices
16
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Signature oracle
From: [email protected]: [email protected]: text/html
<style>@media (max-device-width: 834px) {.covert {visibility: hidden;}}
@media (min-device-width: 835px) {* {visibility: hidden;}.covert {visibility: visible}}
</style>What's up Johnny?<div class="covert">I hereby declare war.</div>
but show on desktop devices
16
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I'm fine, thanks.
On 01/05/19 09:53, Eve wrote:> What's up Johnny?
Re: What's up Johnny?
17
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I'm fine, thanks.
On 01/05/19 09:53, Eve wrote:> What's up Johnny?
Re: What's up Johnny?
Reply email sent from Johnny’s mobile phone
17
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I'm fine, thanks.
On 01/05/19 09:53, Eve wrote:> What's up Johnny?
Re: What's up Johnny?
Reply email sent from Johnny’s mobile phone
17
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I'm fine, thanks.
On 01/05/19 09:53, Eve wrote:> What's up Johnny?
Re: What's up Johnny?
I hereby declare war.
Signed email received on a desktop device
Reply email sent from Johnny’s mobile phone
17
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Conditional rules
18
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• Targeting device type (@media)
Conditional rules
18
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• Targeting device type (@media)• Targeting email client (@supports)
Conditional rules
18
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• Targeting device type (@media)• Targeting email client (@supports)• Targeting user account (@document)
Conditional rules
18
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• Targeting device type (@media)• Targeting email client (@supports)• Targeting user account (@document)
Conditional rules
18
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1. Introduction2. Attacks on Encryption3. Attacks on Signatures4. Evaluation5. Mitigation
Overview
19
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1. Introduction2. Attacks on Encryption3. Attacks on Signatures4. Evaluation5. Mitigation
Overview
19
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OS ClientDecryption Signatures
S/MIME PGP S/MIME PGP
Windows
ThunderbirdOutlookWin. 10 MailWin Live MailThe Bat!PostboxeM Client
Linux
KMailEvolutionTrojitáClawsMutt
macOSApple MailMailMateAirmail
iOS Mail App
Android
K-9 MailR2Mail2MailDroidNine
Web
Exchange/OWARoundcubeHorde/IMPMailpile
● Plaintext can be completely hidden
◐ Plaintext merged with attacker-text
○ No vulnerabilities found
– Cryptosystem not available
Decryption oracles
● Covert rules kept in reply message
◐ Covert rules only for received mail
Signature oracles
20
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OS ClientDecryption Signatures
S/MIME PGP S/MIME PGP
Windows
Thunderbird ●Outlook ○Win. 10 Mail ○Win Live Mail ○The Bat! ○Postbox ●eM Client ○
Linux
KMail ◐Evolution ◐Trojitá ◐Claws ◐Mutt ◐
macOSApple Mail ●MailMate ●Airmail ●
iOS Mail App ●
Android
K-9 Mail –R2Mail2 ○MailDroid ○Nine ○
Web
Exchange/OWA ○Roundcube –Horde/IMP ○Mailpile –
● Plaintext can be completely hidden
◐ Plaintext merged with attacker-text
○ No vulnerabilities found
– Cryptosystem not available
Decryption oracles
● Covert rules kept in reply message
◐ Covert rules only for received mail
Signature oracles
20
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OS ClientDecryption Signatures
S/MIME PGP S/MIME PGP
Windows
Thunderbird ● ●Outlook ○ ○Win. 10 Mail ○ –Win Live Mail ○ –The Bat! ○ ○Postbox ● ●eM Client ○ ○
Linux
KMail ◐ ◐Evolution ◐ ◐Trojitá ◐ ◐Claws ◐ ◐Mutt ◐ ◐
macOSApple Mail ● ●MailMate ● ●Airmail ● ●
iOS Mail App ● –
Android
K-9 Mail – ○R2Mail2 ○ ●MailDroid ○ ○Nine ○ –
Web
Exchange/OWA ○ –Roundcube – ◐Horde/IMP ○ ○Mailpile – ○
● Plaintext can be completely hidden
◐ Plaintext merged with attacker-text
○ No vulnerabilities found
– Cryptosystem not available
Decryption oracles
● Covert rules kept in reply message
◐ Covert rules only for received mail
Signature oracles
20
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OS ClientDecryption Signatures
S/MIME PGP S/MIME PGP
Windows
Thunderbird ● ● ●Outlook ○ ○ ◐Win. 10 Mail ○ – ◐Win Live Mail ○ – ●The Bat! ○ ○ ○Postbox ● ● ●eM Client ○ ○ ◐
Linux
KMail ◐ ◐ ○Evolution ◐ ◐ ◐Trojitá ◐ ◐ ◐Claws ◐ ◐ ○Mutt ◐ ◐ ○
macOSApple Mail ● ● ◐MailMate ● ● ●Airmail ● ● ●
iOS Mail App ● – ●
Android
K-9 Mail – ○ –R2Mail2 ○ ● ◐MailDroid ○ ○ ●Nine ○ – ●
Web
Exchange/OWA ○ – ●Roundcube – ◐ ◐Horde/IMP ○ ○ ◐Mailpile – ○ –
● Plaintext can be completely hidden
◐ Plaintext merged with attacker-text
○ No vulnerabilities found
– Cryptosystem not available
Decryption oracles
● Covert rules kept in reply message
◐ Covert rules only for received mail
Signature oracles
20
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OS ClientDecryption Signatures
S/MIME PGP S/MIME PGP
Windows
Thunderbird ● ● ● ●Outlook ○ ○ ◐ ◐Win. 10 Mail ○ – ◐ –Win Live Mail ○ – ● –The Bat! ○ ○ ○ ○Postbox ● ● ● ●eM Client ○ ○ ◐ ◐
Linux
KMail ◐ ◐ ○ ○Evolution ◐ ◐ ◐ ◐Trojitá ◐ ◐ ◐ ◐Claws ◐ ◐ ○ ○Mutt ◐ ◐ ○ ○
macOSApple Mail ● ● ◐ ◐MailMate ● ● ● ●Airmail ● ● ● ●
iOS Mail App ● – ● –
Android
K-9 Mail – ○ – ●R2Mail2 ○ ● ◐ ◐MailDroid ○ ○ ● ●Nine ○ – ● –
Web
Exchange/OWA ○ – ● –Roundcube – ◐ ◐ ◐Horde/IMP ○ ○ ◐ ◐Mailpile – ○ – ○
● Plaintext can be completely hidden
◐ Plaintext merged with attacker-text
○ No vulnerabilities found
– Cryptosystem not available
Decryption oracles
● Covert rules kept in reply message
◐ Covert rules only for received mail
Signature oracles
20
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OS ClientDecryption Signatures
S/MIME PGP S/MIME PGP
Windows
Thunderbird ● ● ● ●Outlook ○ ○ ◐ ◐Win. 10 Mail ○ – ◐ –Win Live Mail ○ – ● –The Bat! ○ ○ ○ ○Postbox ● ● ● ●eM Client ○ ○ ◐ ◐
Linux
KMail ◐ ◐ ○ ○Evolution ◐ ◐ ◐ ◐Trojitá ◐ ◐ ◐ ◐Claws ◐ ◐ ○ ○Mutt ◐ ◐ ○ ○
macOSApple Mail ● ● ◐ ◐MailMate ● ● ● ●Airmail ● ● ● ●
iOS Mail App ● – ● –
Android
K-9 Mail – ○ – ●R2Mail2 ○ ● ◐ ◐MailDroid ○ ○ ● ●Nine ○ – ● –
Web
Exchange/OWA ○ – ● –Roundcube – ◐ ◐ ◐Horde/IMP ○ ○ ◐ ◐Mailpile – ○ – ○
● Plaintext can be completely hidden
◐ Plaintext merged with attacker-text
○ No vulnerabilities found
– Cryptosystem not available
Decryption oracles
● Covert rules kept in reply message
◐ Covert rules only for received mail
Signature oracles
20
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1. Introduction2. Attacks on Encryption3. Attacks on Signatures4. Evaluation5. Mitigation
Overview
21
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1. Introduction2. Attacks on Encryption3. Attacks on Signatures4. Evaluation5. Mitigation
Overview
21
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Decryption oracles
22
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• Accepting ASCII text only
Decryption oracles
22
![Page 95: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/95.jpg)
• Accepting ASCII text only
Decryption oracles
22
![Page 96: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/96.jpg)
• Accepting ASCII text only• Enforcing digital signatures
Decryption oracles
22
![Page 97: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/97.jpg)
• Accepting ASCII text only• Enforcing digital signatures
Decryption oracles
22
![Page 98: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/98.jpg)
• Accepting ASCII text only• Enforcing digital signatures• Warn on partial encryption
Decryption oracles
22
![Page 99: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/99.jpg)
• Accepting ASCII text only• Enforcing digital signatures• Warn on partial encryption
Decryption oracles
22
![Page 100: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/100.jpg)
• Accepting ASCII text only• Enforcing digital signatures• Warn on partial encryption• All-or-Nothing Encryption
Decryption oracles
22
![Page 101: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/101.jpg)
• Accepting ASCII text only• Enforcing digital signatures• Warn on partial encryption• All-or-Nothing Encryption
Decryption oracles
Root causes: long-term keys +ciphertext usage out-of-context
22
![Page 102: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/102.jpg)
Signing oracles
23
![Page 103: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/103.jpg)
• Dropping CSS Support
Signing oracles
23
![Page 104: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/104.jpg)
• Dropping CSS Support
Signing oracles
23
![Page 105: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/105.jpg)
• Dropping CSS Support• Only ASCII Text in replies
Signing oracles
23
![Page 106: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/106.jpg)
• Dropping CSS Support• Only ASCII Text in replies• Remove styles from replies
Signing oracles
23
![Page 107: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/107.jpg)
Conclusion
24
![Page 108: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/108.jpg)
• Crypto is not enough, bypasses exist
Conclusion
24
![Page 109: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/109.jpg)
• Crypto is not enough, bypasses exist• 22 of 24 tested clients are vulnerable
Conclusion
24
![Page 110: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/110.jpg)
• Crypto is not enough, bypasses exist• 22 of 24 tested clients are vulnerable• Building security on top of email is hard
Conclusion
24
![Page 111: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/111.jpg)
• Crypto is not enough, bypasses exist• 22 of 24 tested clients are vulnerable• Building security on top of email is hard
Conclusion
Thank you! Questions?Exploits: github.com/RUB-NDS/Covert-Content-Attacks
24
![Page 112: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/112.jpg)
HTML and CSS support in various email clients
![Page 113: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/113.jpg)
Proprietary conditional features
![Page 114: Re: What’s up Johnny? - DEF CON CON 27/DEF CON 27... · S/MIME PGP S/MIME PGP Windows Thunderbird Outlook Win. 10 Mail Win Live Mail The Bat! Postbox eM Client Linux KMail Evolution](https://reader034.vdocuments.us/reader034/viewer/2022050214/5f609a4107ac8247b74bd66e/html5/thumbnails/114.jpg)
Blinding options