Post on 03-Jan-2016
description
transcript
A Security Primer
Security Topics
PGP S/MIME
SSL TLS
IPSec
Cryptography
Symmetric Key
Public Key
Algorithms
Encryption
Digital Signatures
Certificates
Algorithms
Encryption
Key Mgmt
Need for message securityPrivacy
Am I sure no body else knows this?Authentication
Am I sure that the sender is genuine and not an imposter?Integrity
Am I sure that the message has not been tampered on its way?
Non-repudiationWhat will I do if the sender denies sending the message?
Cryptography
Cryptography Jargon
Cryptography means “Secret Writing”Original message – plaintextEncrypted message – ciphertextEncryption and decryption algorithms – ciphersThe number value that the cipher operates on –key
TypesSymmetric key cryptography Public key cryptography
Symmetric Key Cryptography
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Encrypt
Network
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Decrypt
Shared secret key
• Features– Same key used by sender and receiver– Algorithm for decryption is inverse of the
algorithm used for encryption
Alice Bob
1 2
Symmetric Key (contd.)Algorithms
DES (Data Encryption Standard)Triple DES
AdvantagesEfficient algorithms (takes less time to encrypt and
decrypt)Simple
DisadvantagesEach pair must have unique keys. i.e. N people will
require N(N-1)/2 keysDistribution of keys between two parties can be difficult
Public Key Cryptography
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Encrypt
Network
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Decrypt
Bob’s public key
Alice Bob
Bob’s private key
To the public
1
2
• Features– There are two keys: a private key and a public key– The private key is kept by the receiver and the
public key is announced to the public
Public Key (contd.)Algorithms
RSA (Rivest, Shamir and Adleman)
AdvantagesNeed to distribute only the public key. Private key can be
safely keptLesser number of keys i.e. 1 million users may need only
2 million keys (as compared to 500 billion, if they use symmetric key cryptography)
DisadvantagesComplex algorithms Association between the public key and the entity must
be verified (need for certificates)
Digital SignaturesFeatures
Enables integrity, authentication and non-repudiationPrivate keys are used to sign a message (or hash)Public keys are used to verify the signatures
Hash FunctionsSigning the whole message is inefficientHash functions are used to create a unique digest of the
messagePopular hashing algorithms are SHA-1 (secure hash
algorithm) and MD5 (message digest)
Digital Signatures (contd.)
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Alice
Hash Function
Digest
Encrypt
Alice’s private key
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Signed Digest
Message plus Signed Digest
To Bob
1
2
3
Sender site
Digital Signatures (contd.)
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Receiver site
Bob
From Alice
Decrypt Hash Function
Digest
Alice’s public key
DigestX
Compare
4 5
6
Key ManagementIn symmetric key systems:
We need a mechanism to share the key between sender and receiver, and also reduce the number of keys
In some cases, public key systems also use symmetric key to encrypt a message and encrypt the key using public key
Solution: session keys. Symmetric keys are created for a session and destroyed when the session is over
Techniques for key management:Deffie Hellman methodKey distribution center (Needham-Schroeder protocol and
Otway-Rees protocol)
Key Management (contd.)In public key systems:
Alice needs to know whether Bob’s public key is genuineSolution: Certificates
Bob goes to a Certification Authority (CA), e.g. VeriSign, which binds Bob’s public key to an entity called certificate.
Certificate is signed by CA, which has a well known public key, and hence cannot be forged.
Alice can verify the CA’s signature and hence be sure about Bob’s public key
Certificates Certificate is described by X.509 protocol X.509 uses ASN.1 (Abstract Syntax Notation 1) to define the
fields X.509 fields:
Field Explanation
Version Version number of X.509
Serial Number The unique identifier used by the CA
Signature The certificate signature
Issuer The name of the CA defined by X.509
Validity Period
Start and end period that certificate is valid
Subject Name The entity whose public key is being certified
Public Key The subject public key and the algorithms that use it
Chain of Trust Query propagation similar to DNS queries At any level, the CA can certify performance of CAs in the
next level i.e. level-1 CA can certify level-2 CAs. Thumb-rule: Everyone trusts Root CA
Root CA
Level-1CA 1
Level-2CA 3
Level-2CA 4
Level-2CA 5
Level-2CA 6
Level-2CA 2
Level-2CA 1
Level-1CA 2
Security at IP Level
IPSec – IP Security Secures the IP packet by adding additional header
Selection of encryption, authentication and hashing methods left to the user
It requires a logical connection between two hosts, achieved using Security Association (SA)
An SA is defined by:A 32-bit security parameter index (SPI)Protocol type: Authentication Header (AH) Or Encapsulating
Security Payload (ESP)The source IP address
IP HeaderIPSec Header Rest of the PacketNew IP Header
IP Header IPSec Header Rest of the Packet Transport Mode
Tunnel Mode
OR
Security at Transport Layer
Secure Sockets Layer (SSL) Developed by Netscape Used to establish secure connection between two parties Protocol similar to TLS (p.t.o) OpenSSL (www.openssl.org) provides libraries which
implement SSL and TLS Several application layer security protocols run on top of
SSL. E.g. Secure HTTP (https)
Transport Layer Security (TLS)
Designed by IETF; derived from SSL Lies on top of Transport layer Uses two protocols:
Handshake Protocol
– Data exchange protocol
– Uses secret key to encrypt data.
– Secret key already shared during handshake
Hello
Certificate
Secret key
End Handshaking
Encrypted Ack
Client Server
Transport Layer Security (TLS)
Designed by IETF; derived from SSL Lies on top of Transport layer Uses two protocols:
Handshake Protocol
– Data exchange protocol
– Uses secret key to encrypt data.
– Secret key already shared during handshake
Hello
Certificate
Secret key
End Handshaking
Encrypted Ack
Client Server
Browser sends a hello message that includes TLS version and other
preferences
Transport Layer Security (TLS)
Designed by IETF; derived from SSL Lies on top of Transport layer Uses two protocols:
Handshake Protocol
– Data exchange protocol
– Uses secret key to encrypt data.
– Secret key already shared during handshake
Hello
Certificate
Secret key
End Handshaking
Encrypted Ack
Client Server
Server sends a certificate that has its
public key
Transport Layer Security (TLS)
Designed by IETF; derived from SSL Lies on top of Transport layer Uses two protocols:
Handshake Protocol
– Data exchange protocol
– Uses secret key to encrypt data.
– Secret key already shared during handshake
Hello
Certificate
Secret key
End Handshaking
Encrypted Ack
Client Server
Browser verifies the certificate. It generates a
session key, encrypts with server’s public key
and sends it to the server
Transport Layer Security (TLS)
Designed by IETF; derived from SSL Lies on top of Transport layer Uses two protocols:
Handshake Protocol
– Data exchange protocol
– Uses secret key to encrypt data.
– Secret key already shared during handshake
Hello
Certificate
Secret key
End Handshaking
Encrypted Ack
Client Server
Browser sends handshake terminating message, encrypted by
the secret key
Transport Layer Security (TLS)
Designed by IETF; derived from SSL Lies on top of Transport layer Uses two protocols:
Handshake Protocol
– Data exchange protocol
– Uses secret key to encrypt data.
– Secret key already shared during handshake
Hello
Certificate
Secret key
End Handshaking
Encrypted Ack
Client Server
Server decrypts secret key with its private key.
Uses secret key to decode message ad sends encrypted ack
Security at Application Layer
Pretty Good Privacy (PGP)
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Alice
Hash Function
Digest
Encrypt
Alice’s private key
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Signed Digest
Message plus Signed Digest
Encrypted (secret key & message + digest) to Bob
1
2
3Encrypt
Bob’s public key
Encrypt
One-time secret key
+
4
5
6
Sender site
Pretty Good Privacy (PGP)
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Alice
Hash Function
Digest
Encrypt
Alice’s private key
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Signed Digest
Message plus Signed Digest
Encrypted (secret key & message + digest) to Bob
1
2
3Encrypt
Bob’s public key
Encrypt
One-time secret key
+
4
5
6
Sender site
Email message is hashed to create digest
Pretty Good Privacy (PGP)
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Alice
Hash Function
Digest
Encrypt
Alice’s private key
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Signed Digest
Message plus Signed Digest
Encrypted (secret key & message + digest) to Bob
1
2
3Encrypt
Bob’s public key
Encrypt
One-time secret key
+
4
5
6
Sender site
Digest is encrypted using Alice’s private key
Pretty Good Privacy (PGP)
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Alice
Hash Function
Digest
Encrypt
Alice’s private key
+110.ico
Signed Digest
Message plus Signed Digest
Encrypted (secret key & message + digest) to Bob
1
2
3Encrypt
Bob’s public key
Encrypt
One-time secret key
+
4
5
6
Sender site
Signed digest added to the message
Pretty Good Privacy (PGP)
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Alice
Hash Function
Digest
Encrypt
Alice’s private key
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Signed Digest
Message plus Signed Digest
Encrypted (secret key & message + digest) to Bob
1
2
3Encrypt
Bob’s public key
Encrypt
One-time secret key
+
4
5
6
Sender site
The message and digest are encrypted using one
time secret key created by Alice
Pretty Good Privacy (PGP)
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Alice
Hash Function
Digest
Encrypt
Alice’s private key
+110.ico
Signed Digest
Message plus Signed Digest
Encrypted (secret key & message + digest) to Bob
1
2
3Encrypt
Bob’s public key
Encrypt
One-time secret key
+
4
5
6
Sender site
The secret key is encrypted using Bob’s public key
Pretty Good Privacy (PGP)
110.ico
Alice
Hash Function
Digest
Encrypt
Alice’s private key
+110.ico
Signed Digest
Message plus Signed Digest
Encrypted (secret key & message + digest) to Bob
1
2
3Encrypt
Bob’s public key
Encrypt
One-time secret key
+
4
5
6
Sender site
The encrypted message, digest and secret key is sent
to Bob
PGP (contd.)
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Receiver site
Bob
Decrypt Hash Function
Digest
Alice’s public key
DigestX
Compare
9 10
11
Encrypted (secret key & message + digest)
Bob’s private key
Decrypt
Decrypt
Encrypted (message + digest)
One-time secret key
7
8
PGP (contd.)
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Receiver site
Bob
Decrypt Hash Function
Digest
Alice’s public key
DigestX
Compare
9 10
11
Encrypted (secret key & message + digest)
Bob’s private key
Decrypt
Decrypt
Encrypted (message + digest)
One-time secret key
7
8
Bob decrypts the secret key with his private key
PGP (contd.)
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Receiver site
Bob
Decrypt Hash Function
Digest
Alice’s public key
DigestX
Compare
9 10
11
Encrypted (secret key & message + digest)
Bob’s private key
Decrypt
Decrypt
Encrypted (message + digest)
One-time secret key
7
8
Bob decrypts the encrypted message and digest using the decrypted secret key
PGP (contd.)
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Receiver site
Bob
Decrypt Hash Function
Digest
Alice’s public key
DigestX
Compare
9 10
11
Encrypted (secret key & message + digest)
Bob’s private key
Decrypt
Decrypt
Encrypted (message + digest)
One-time secret key
7
8
Bob decrypts the encrypted digest with Alice’s public key
PGP (contd.)
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Receiver site
Bob
Decrypt Hash Function
Digest
Alice’s public key
DigestX
Compare
9 10
11
Encrypted (secret key & message + digest)
Bob’s private key
Decrypt
Decrypt
Encrypted (message + digest)
One-time secret key
7
8
Bob hashes the received message to create a digest
(for message integrity)
PGP (contd.)
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Receiver site
Bob
Decrypt Hash Function
Digest
Alice’s public key
DigestX
Compare
9 10
11
Encrypted (secret key & message + digest)
Bob’s private key
Decrypt
Decrypt
Encrypted (message + digest)
One-time secret key
7
8
The two digests are compared, thus providing
authentication and integrity
Sample PGP SignatureFrom: alice@wonderland.comDate: Mon, 16 Nov 1998 19:03:30 -0600Subject: Message signed with PGPMIME-Version: 1.0Content-Type: text/plain; charset=US-ASCIIContent-Transfer-Encoding: 7bitContent-Description: "cc:Mail Note Part"
-----BEGIN PGP SIGNED MESSAGE-----
Bob,
This is a message signed with PGP, so you can see how much overhead PGPsignatues introduce. Compare this with a similar message signed with S/MIME.
Alice
-----BEGIN PGP SIGNATURE-----Version: PGP for Personal Privacy 5.0Charset: noconv
iQCVAwUBM+oTwFcsAarXHFeRAQEsJgP/X3noON57U/6XVygOFjSY5lTpvAduPZ8MaIFalUkCNuLLGxmtsbwRiDWLtCeWG3k+7zXDfx4YxuUcofGJn0QaTlk8b3nxADL0O/EIvC/k8zJ6aGaPLB7rTIizamGOt5n6/08rPwwVkRB03tmT8UNMAUCgoM02d6HXrKvnc2aBPFI==mUaH-----END PGP SIGNATURE-----
S/MIME Working principle similar to PGP S/MIME uses multipart MIME type to include the cryptographic
information with the message S/MIME uses Cryptographic Message Syntax (CMS) to specify the
cryptographic information Creating S/MIME message:
MIME Entity
CMS Object S/MIMECertificates
Algo identifiers
CMS Processing
MIME Wrapping
Sample SMIME SignatureFrom: alice@wonderland.comDate: Mon, 16 Nov 1998 19:03:08 -0600Subject: Message signed with S/MIMEMIME-Version: 1.0Content-Type: multipart/mixed; boundary="simple boundary"
--simple boundaryContent-Type: text/plain; charset=US-ASCIIContent-Transfer-Encoding: 7bitContent-Description: "cc:Mail Note Part"
Bob,
This is a message signed with S/MIME, so you can see how much overhead S/MIMEsignatures introduce. Compare this with a similar message signed with PGP.
Alice
--simple boundaryContent-Type: application/octet-stream; name="smime.p7s"Content-Transfer-Encoding: base64Content-Disposition: attachment; filename="smime.p7s"
MIIQQwYJKoZIhvcNAQcCoIIQNDCCEDACAQExCzAJBgUrDgMCGgUAMAsGCSqGSIb3DQEHAaCCDnwwggnGMIIJL6ADAgECAhBQQRR9a+DX0FHXfQOVHQhPMA0GCSqGSIb3DQEBBAUAMGIxETAPBgNVBAcTCEludGVybmV0MRcwFQYDVQQKEw5WZXJpU2lnbiwgSW5jLjE0MDIGA1UECxMrVmVyaVNpZ24gQ2xhc3MgMSBDQSAtIEluZGl2aWR1YWwgU3Vic2NyaWJlcjAeFw05NzAxMjcwMDAwMDBaFw05ODAxMjcyMzU5NTlaMIIBFzERMA8GA1UEBxMISW50ZXJuZXQxFzAVBgNVBAoTDlZlcmlTaWduLCBJbmMuMTQwMgYDVQQLEytWZXJpU2lnbiBDbGFzcyAxIENBIC0gSW5kaXZpZHVhbCBTdWJzY3JpYmVyMUYwRAYD
Sample SMIME 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
--simple boundary--
References
References Overview of cryptography:
www.rsalabs.com/faq/ http://www.faqs.org/faqs/cryptography-faq/part06/
Implementation of SSL and TSL: www.openssl.org
S/MIME Internet task force: www.imc.org/ietf-smime/index.html
Relationship between S/MIME and PGP/MIME: www.imc.org/smime-pgpmime.html