Java Crypto

csci5931 Web Security 1

GS: Chapter 3

Encryption, Authentication and Java Cryptography


Cryptography & Java

A. Encryption

B. Authentication

C. Java Cryptography


Encryption Encryption Basics:

An algorithm (or cipher) and a key are required in order to encrypt or decrypt messages.

Example: the Caesar cipher (p.34)o A symmetric, stream ciphero Exercise: Encrypt “DDAY” using Caesar cipher

(5).o Answer: “IIFD”.o Q: What is the algorithm?o Q: What is the key?o Q: How would the cipher be decrypted?


Encryption Symmetric Encryptions:

Both the encrypter and the decrypter share the same key.

Key space: The set of possible keys that work with a cipher; determined by the number of bits used in the cipher.

The larger the key space is, the more secure the encryption will be.

Each additional bit added to the key length doubles its security.


Encryption

Symmetric Encryptions: Two types of symmetric ciphers: block ciphers and

stream ciphers. Examples of symmetric encryptions:

o DES (Data Encryption Standard) & TripleDES: block ciphers

o Blowfish: a faster and more secure replacement of DES

o RC4 (Rivest’s Code 4): a stream ciphero AES (Advanced Encryption Standard): a block

cipher


Encryption Limitations of Symmetric Encryptions:

Key distribution can be a vulnerability. If the key is exposed, the encrypted message and all

future communication using the same key will suffer

the eavesdropping attack. Key management problems: distribution, update,

revoking


Encryption Asymmetric Encryptions:

Also known as ‘public key encryption’ Messages encrypted with the public key can only be

decrypted by the corresponding private key. The public key can be made known to the public, but

the private key is kept as secret and only known to the owner of the key.

Examples of asymmetric encryption algorithms:o Merkel Hellman Knapsackso RSA: Rivest, Shamir, Adlemano El Gamal


Encryption Limitations of asymmetric Encryptions:

Asymmetric encryption requires much larger keys than symmetric encryption.

o A 1024-bit asymmetric key ~= a 128-bit symmetric key

o Why?

Asymmetric encryption is much slower (~ 1000 times

slower) than symmetric encryption.

It is subject to man-in-the-middle attack.

Solution? Digital certificates (Ch. 6)


Encryption Session-key Encryption

A session-key is a symmetric key that is used to encrypt the plaintext message. The session key itself is encrypted using a public key.

Sender: C = Spub ( S ) + Sencrypt (message) Recipient

Recipient: Spriv ( Spub (S) ) SSdecrypt (Sencrypt (message)) message

Alternatively, the session key may be assigned an expiration time and be used over several sessions.


Encryption Examples of Session-key Encryption

PGP (Pretty Good Privacy): Originally (1991) used to encrypt e-mail using

session-key encryptionSupports RSA, TripleDES, etc.http://www.pgp.com/

S/MIME (Secure/MIME):Invented by RSA to secure e-mailBacked by Microsoft, RSA, and AOL

SSL/TLS (Secure Socket Layer/Transport Layer Security): Ch. 9

Originally an attempt to secure TCP/IP traffic using encryptions

http://www.pgp.com/

http://www.pgp.com/

http://www.pgp.com/


Encryption Key Agreement Algorithm

A key agreement algorithm takes the private and the public keys of two distinct parties (Apriv + Bpub or Apub + Bpriv) and generates a common shared secret key, which is then used to generate a session key. See the diagram on p.41.

Diffie-Hellman Key Agreement Algorithm: The first ever public key encryption

Allows two parties to independently generate the shared key; The session key is never transmitted.

References: See http://www.apocalypse.org/pub/u/seven/diffie.html IETF RFC2631: http://www.ietf.org/rfc/rfc2631.txt

http://www.apocalypse.org/pub/u/seven/diffie.html

http://www.ietf.org/rfc/rfc2631.txt


Encryption

Strength of Encryption Algorithms Two factors:

The algorithm used + The size of the key space

See the tables comparing symmetric ciphers (p.42) and asymmetric ciphers (p.43)


Alternative Data-hiding Methods Steganography: hiding messages inside another

message or in a picture. See “Steganography: Hidden Data”. By Deborah

Radcliff. ComputerWorld. June 10, 2002.

Elliptic Curve Cryptography (ECC): based on the elliptic curve logarithm problem; a more efficient public key encryption (faster, smaller key size)

An intro: http://world.std.com/~dpj/elliptic.html

Codes, one-time pads, etc.

http://world.std.com/~dpj/elliptic.html


Authentication The process of determining the authenticity of a

message or user. Methods:A. Message Digest

a check value generated from a document, usually generated by a hash function

to prove that the data in the document has not been tampered with.

Commonly used for password authentication (i.e., one-way authentication)

Examples: MD4, MD5, SHA (secure hash algorithm) Any problem? Man-in-the-middle attack Why?


Authentication MethodsB. MAC (Message Authentication Codes)

A message digest created with a key

Typically used for data verification in a context where a secure connection is already available.

Example: SSL uses MACs to verify the data received, using a secret key that is exchanged at the beginning of the session.

Example MACs:o HmacMD5 (Hashing MAC using MD5)o HmacSHA1 (Hashing MAC using SHA-1)


Authentication MethodsC. Digital Signatures

Based on public key encryption Computed with a person’s private key and verified

with the person’s public key An example of creating a digital signature: p.48

1. The sender applies a message digest algorithm to get a message digest (md) out of the message to be sent.

2. The message digest is then encrypted by the person’s private key. The ciphertext is the digital signature (ds).

To check the digital signature:1. The recipient applies the digest algorithm to get a message

digest (md-2).2. The recipient decrypts the ds using the sender’s public key. 3. The output from step 2 is verified against md-2.


Authentication Methods

D. Digital Certificates Purpose: To authenticate a person’s public key

“Vouching”: one party certifies that another party’s identity is authentic. e.g., passport, id cards

A digital certificate for A is A’s public key plus some identifying information, signed by the private key of a certification authority (CA) verifying A’s identity.

Other example usage of certificates:o To authenticate a host/server (e.g., SSL certificates)o To sign and encrypt e-mail


Authentication Methods

D. Digital Certificates (Cont.) Certificates are often chained. That is, a CA may be

authenticated by a root CA.

The top CA of a certificate chain must be self-signed.

Verisign has been accepted as the top CA.

Example of certificate chaining: Both Internet Explorer and Netscape Communicator include certificates from Verisign in their install. So when the browser makes an SSL connection to a server, if the server presents a certificate that is signed by Verisign, the server’s certificate will be automatically accepted.


Cryptanalysis The practice of analyzing and breaking cryptography

Mehtods:

Brute force attack versus the key space

Common cryptanalytic tools: Frequency distribution, Digram/trigram study, IC, Repeated patterns, Probable letters

4 cryptanalytic cases:

1. Ciphertext only Ciphertext-only attack

2. Full or partial plaintext Known plaintext attack Probable plaintext analysis

3. Ciphertext of any plaintext Chosen plaintext attack

4. Algorithm + Ciphertext Chosen ciphertext attack


Key Management (storage)

A dilemma: Keys must be securely stored while allowing users easy access when necessary.

A typical solution is to encrypt the stored keys with passwords and then protect the storage with the OS access control.

A key storage is an attractive target for attack. The smart card solution: A smart card stores a private key

and a certificate, which can be used to encrypt and/or decrypt information.

An example of smart card solution: See Protection of Keys (RSA vs nCipher)


Cryptographical Protocols Cryptographical protocols determine the exact order and

way in which each algorithm must be used in order to maximize security.

Examples of protocols:– Distribution of keys,

– Certificates, Digital signatures,

– Key escrow,

– Mental poker,

– Electronic voting,

– oblivious transfer, contract signing,

– certified mail


JCA/JCE Java Cryptography Architecture (JCA) is part of the Java 2

run-time environment. java.security.*

JCE (Java Cryptography Extension), on the other hand, is an extension to the JCA. JCE adds encryption and decryption APIs to the JCA. java.crypto.*

Major classes defined in JCA: MessageDigest, Signature, KeyPairGenerator, KeyFactory, CertificateFactory, KeyStore, AlgorithmParameters, AlgorithmParameterGenerator, SecureRandom, …


JCA/JCE A cryptographic service provider implements various

cryptographic algorithms.

See page 54 for a list of algorithms implemented in the SUN provider (sun.security.provider.Sun), Java 2 (v1.2).

A second provider, the RSAJCA provider (com.sun.rsajca.Provider) is shipped with JDK v1.3, to provide RSA-specific cryptos.


JCA An example of using MessageDigest in the JCA:

1. Get an instance of a message digest.MessageDigest myMessageDigest =

MessageDigest.getInstance (“MD5”);Or MessageDigest myMessageDigest =

MessageDigest.getInstance (“MD5”,”Sun”);

2. Add data to be digested.myMessageDigest.update (myData);

3. Get the digest.byte [ ] signatureBytes =

myMessageDigest.digest ( );


JCE Major JCE classes:

Cipher, KeyAgreement, KeyGenerator, MAC, SecretKey, SecretKeyFactory

JCE needs to be separately downloaded and installed if you have JDK older than v1.4. For JDK1.4 or higher, JCE is an integrated component.

See http://java.sun.com/products/jce/index-14.html for more details.


JCE Installation of JCE security provider

Sample programs: http://nas.cl.uh.edu/yang/teaching/csci5931webSecurity/JC

E%20provider.htm

Visit http://sce.cl.uh.edu/yang/teaching/proJavaSecurityCode.ht

ml and download all the sample programs from the book.


Next

Symmetric Encryption (GS: 4) Asymmetric Encryption (GS: 5)

Technology

Java Crypto