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COSC362 > Lecture 20: Email security > Flashcards

Lecture 20: Email security Flashcards

1
Q

What are the two types of link security?

A

DKIM

STARTTLS

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2
Q

What are the two types of end-to-end security?

A

PGP

S/MIME

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3
Q

What does DKIM stand for?

A

Domain Keys Identified Mail

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4
Q

What does S/MIME stand for?

A

Secure/Multipurpose Internet Mail Extension

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5
Q

What does SMTP stand for?

A

Single message transfer protocol

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6
Q

What is SMTP?

A

a mail transmission protocol to send an email from a source to a destination

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7
Q

What are POP and IMAP?

A

mail access protocols to allow a message user agent (MUA) to download an email from a message transfer agent (MTA)

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8
Q

What does MUA stand for?

A

message user agent

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9
Q

What does MTA stand for?

A

message transfer agent

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10
Q

What does the MUA do?

A

connects a client to a mail system

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11
Q

What does the MUA when using SMTP?

A

to send a mail to a message submission agent (MSA)

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12
Q

What is a MSA?

A

message submission agent

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13
Q

What does the MUA do when using POP or IMAP?

A

to retrieve the mail from the message store (MS)

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14
Q

What does MS stand for?

A

message store

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15
Q

What does MHS stand for?

A

message handling system

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16
Q

What does the MHS do?

A

transfers a message from MSA to MS via one or more message transfer agents(MTAs)

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17
Q

Give the diagram for the architecture i.t.o email security requirements

IMPORTANT

A

See slide 7 in set 20

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18
Q

Comment on potential security threats i.t.o email security

A

Considering threats in the usual CIA categories

  • -> Email content may require confidentiality and/or authentication
  • -> Email service availability may be threatened

Metadata in the header is a significant source of information for an attacker

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19
Q

What is spam?

A

Unsolicited bulk email (UBE)

A cheap form of advertising?

Common vector for phishing attacks

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20
Q

What do countermeasures of span typically use?

A

email filtering

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21
Q

Comment on the proposals to implement proof of work for preventing spam

A

The email sender must solve a moderately hard puzzle in order to have the mail accepted into MHS

e.g. Hashcash

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22
Q

What kind of basis is security provided between different agents in the mail system on? What protocols are used?

A

link-by-link basis

STARTTLS and DKIM

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23
Q

What kind of basis is security provided from client to client in the mail system on? What protocols are used?

A

end-to-end basis

PGP and S/MIME

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24
Q

In terms of link and end-to-end security, what is the ideal situation?

A

both are used

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25
Q

What standard is DKIM in?

A

RFC 6376 (2011)

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26
Q

What does DKIM allow?

A

the sending mail domain to sign an outgoing mail using RSA signatures

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27
Q

What can verify the origin of mail in DKIM?

A

receiving domain

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28
Q

What uses DKIM?

A

Widely used by prominent email providers, including Gmail

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29
Q

What does DKIM help to prevent?

A

email spoofing, and so to reduce spams and phishing

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30
Q

What is the public key of the sending domain retrieved using in DKIM?

A

a DNS

31
Q

What does DNS stand for?

A

domain name system

32
Q

What does STARTTLS extend?

A

Extending mail protocols SMTP, POP an IMAP to run over TLS connections

33
Q

What type of security does STARTTLS provide?

A

link-by-link security, but not end-to-end security

34
Q

What is opportunistic TLS?

A

extensions in plain text communication protocols, which offer a way to upgrade a plain text connection to an encrypted (TLS or SSL) connection instead of using a separate port for encrypted communication

35
Q

What type of use of TLS encryption security is STARTTLS?

A

opportunistic

36
Q

What standard is IMAP and POP3 in?

A

RFC 2595

37
Q

What standard is SMTP in?

A

RFC 3207

38
Q

What uses STARTTLS?

A

prominent email providers, including Gmail and Microsoft Outlook

39
Q

What is STARTTLS vulnerable to?

A

STRIPTLS attacks

40
Q

What happens in a STRIPTLS attack?

A

An attacker interrupts TLS negotiation, and connection falls back to plaintext transmission

41
Q

What is PGP?

A

Pretty Good Privacy (PGP) is an encryption system used for both sending encrypted emails and encrypting sensitive files

42
Q

What does PGP protect?

A

mail message contents

43
Q

Explain the hybrid encryption in PGP

A

1) A new random “session key” is generated for each message

2) The session key is encrypted with the long-term public key of the recipient

44
Q

What is used for signing in PGP?

A

RSA or DSA

45
Q

Is compression used in PGP?

A

Yes, with Zip

46
Q

What is the coding used in PGP? Why?

A

Coding using radix-64 to ensure that binary strings can be sent in the mail body

47
Q

Comment on the encryption
of session keys in PGP

IMPORTANT

A

encrypted using asymmetric encryption

–> OpenPGP requires the support of Elgamal encryption and recommends the support of RSA encryption

48
Q

Comment on the encryption of message content in PGP

IMPORTANT

A

encrypted using symmetric encryption

–> OpenPGP requires the support of 3DES with 3 keys (168bits in total) and recommends the support of AES-128 andCAST5 (other algorithms are also defined)

49
Q

When is compression applied in PGP?

A

before encryption

50
Q

Can encryption be applied independently of signing in PGP?

A

Yes

51
Q

Why can encryption be applied independently of signing in PGP?

A

no requirement for authenticated encryption

52
Q

Comment on the signing of plaintext messages in PGP

A

Optionally signed with the sender’s private key

–> OpenPGP standard requires the support of RSA signatures and recommends the support of DSA signatures

53
Q

In PGP, what are RSA-signed messages hashed with?

A

SHA1 (in the standard) or with SHA2 hash functions

54
Q

In PGP, in a web of trust, who generates the users’ public/private key pairs?

A

The users generate their own public/private keys pairs

55
Q

In PGP, in a web of trust, what are the public keys available on?

A

distributed key servers

56
Q

In PGP, in a web of trust, who can signed another user’s public key?

A

Any PGP user, indicating their level of trust

57
Q

Who can revoke a user’s key? How?

A

The user, by signing a revocation certificate with the revoked key

–> users can also decide on the key expiration date when generating it

58
Q

Comment on the PGP uptake

A

Around 100 keys added per day on SKS keyserver pool

Growth rate remains linear over past several years

Around 60,000 keys in the strong set of keys with a trust path between any pair of keys

59
Q

What are the 3 main OpenPGP critisms

A

1) outdated cryptographic algorithms still used
- -> SHA1, CAST5, etc

2) No support for SHA3 and authenticated encryption (e.g. GCM)

3) Lots of metadata available to eavesdropper
- -> file length
- -> used encryption algorithms
- -> recipient key identity

60
Q

What are the similar features S/MIME have to PGP?

A

Authentication, integrity, non-repudiation (signature) and confidentiality (encryption) of the message body carried in SMTP messages

61
Q

Comment on the message format used in S/MIME

A

Different, not interoperable message format

62
Q

What is included in each message in S/MIME? Why?

A

Sender’s public key

Used to verify the message

63
Q

What are used instead of Web of Trust in S/MIME?

A

X.509 certificates issued by CAs

64
Q

Which does NIST recommend, S/MIME or PGP? Why?

A

S/MIME rather than PGP because of greater confidence in CA system (compared to Web of Trust)

65
Q

Who supports S/MIME?

A

most popular mail clients

66
Q

Explain the authentication process in S/MIME

IMPORTANT

A

See slide 26 in set 20

67
Q

What are the four guarantees of S/MIME?

IMPORTANT

A

1) RSA guarantee
2) SHA-256 guarantee
3) Public key encryption
4) One-time mechanism

68
Q

Explain the authentication process in S/MIME

IMPORTANT

A

See slide 28 in set 20

69
Q

Outline the RSA guarantee of S/MIME

A

R assured that only the owner of the private key can generates

70
Q

Outline the SHA-256 guarantee of S/MIME

A

R assured that no one else could generate a new digest that matches that h(m), and a signature of m

71
Q

Outline the public key encryption guarantee of S/MIME

A 
No session (content-encryption) key distribution needed
Only R can recover k
72
Q

Outline the one-time mechanism guarantee of S/MIME

A

Symmetric encryption approach is strengthened

73
Q

What is the benefit of combining symmetric cryptography and public key cryptography in S/MIME?

A

allows to reduce encryption time

COSC362 (21 decks)

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