Post on 24-Dec-2015
E-mail Security using EncryptionSecurity Features
• Message Origin Authentication - verifying that the sender is who he or she says they are
• Content Integrity - verifying that the message was not changed after sender sent it
• Content Confidentiality - making certain that only the intended recipient reads the message
• Proof of Delivery - making certain that the message was delivered
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E-mail Security using EncryptionSecurity Features
• Message Sequence Integrity - making certain that all messages were delivered in proper order.
• Non-repudiation of Origin - being able to prove that sender sent a message.
• Non-repudiation of Delivery - being able to prove that a recipient got a message.
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E-mail Security using EncryptionSecurity Features
• Message Security Labeling - labeling a message with handling instructions.
• Message Flow Confidentiality - making certain no one knows who you exchange mail with.
• Secure Access Management - making certain no one uses your e-mail system without being authorized.
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E-mail Security using EncryptionOperation
• All secure e-mail systems work roughly the same way.– Calculate a message digest of the message.
– Encrypt the message digest with sender’s private key.
– Encrypt the mail with a session key (random).
– Encrypt the session key with receiver’s public key.
E-mail Security using EncryptionOperation
• Receiver must:– Decrypt session key with the receiver’s private key.
– Decrypt the message with session key.
– Decrypt message digest with the sender’s public key.
– Calculate a message digest and compare to the one that was sent.• Encrypted message digest serves as both signature and
integrity check.
Sender Functions:
Email message
Create
Message Digest
Private Key
Encrypt MD with Sender’s
Digital Signature
Email message
Encrypt Bundlewith Session Key
(Random Number)
Digit al
Si gna tur e
Em
ai l messa ge
Encrypt withReceiver’s Public Key
{SEND }
1 2
Bundle3
45
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7
1 2
3
4 Set Reply Request
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5
SN
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10 C
onfi
den
tial
Encapsulate Header
Require Private Key to unlock Workstation
SN
Con
fid
enti
al
SNConfidential
Message Sequence No
SecurityLabeling
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Receiver Functions:
Dig
ital
S
i gna
tur e
Em
ail m
essa
ge
{ }
Receive
Decrypt session key withReceiver’s Private Key
1
Decrypt Bundlewith Session Key
2
Digital Signature
Email message
Bundle
3Public Key
Decrypt MD with Sender’s
Message Digest
Create
Message Digest
4Email message SN
Con
fid
enti
al
SN
Con
fid
enti
al
0 = {5
6 Read Message
Compare MD’s
SN Confidential
7Repeat Process in other direction for
Non-Repudiation of Delivery
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