Encryption

Cryptography

•
Secret
-
Key and Public
-
Key Cryptography

•
Cryptographic Primitives

•
Common Public
-
Key Cryptosystems

•
Comparison of Security Levels of PKCS

•
Emerging Trends

•
IEEE P1363

Private
-
Key Cryptography

Secret Message

Private Key

Private Key

Secret Message

Data Encryption

Sender

Receiver

Public
-
Key Cryptography

Secret Message

Recipient’s
Public Key

Secret Message

Recipient’s
Private Key

Interloper’s
Private Key

Cannot decrypt, because
message opens only with
the recipient’s Private key

Data Encryption

Public
-
Key Cryptography

Random Message

Private Key

Garbled Message

Public Key

Signature Verified
Yes / No

Digital Signature

Authentication

B

Party B

Party A

Party A

Party B

Random Message

{random message} B’s Private Key

Random Message

,Yeah! This is B!

{
Random Message

, Yeah! This is B! } B’s Private Key

Random Message

Cryptographic Systems

•
Integer Factorization Systems


p * q = n

•
Discrete Logarithm Systems


y = g
x

( mod p )

•
Elliptic Curve Cryptosystems


Y

2

= x

3

+ ax + b (mod p)


Comparison of Security Levels

•
Current acceptable
security level is
10
12

MIPS

Comparison of security levels ECC and RSA & DSA
0
1000
2000
3000
4000
5000
6000
10000
1000000000
1E+12
1E+20
1E+36
Time to break key (MIPS years)
Key size (bits)
ECC
RSA & DSA
Emerging Trends

•
Secure Channels
-

Secure Socket Layer
(SSL), Private Communications
Technology (PCT)

•
Server Gated Cryptography (SGC)

•
Authenticode

•
CryptoAPI

Secure Socket Layer


Client









Server


Hello

C










Hello

S









Certificate

S

(Client verifies Certificate

S
)

(Client extracts P

S

from Certificate

S
)

(Client selects algorithm A)

(Client generates session key K)


{K} P

S

SpecifyAlgorithm (A)

{Finished

C
} K









SpecifyAlgorithm (A)









{Finished

S
} K











{DATA

C
} K






{DATA

S
} K


CryptoAPI Model

Application

Certificate
Functions

Simplified
Crypto Functions

Base Cryptographic Functions

Microsoft
Base Provider

Smart Card

Cryptographic Service Providers

Crypto API Interface

IEEE P1363

•
Comprehensive
coverage of the
primitive and schemes
of the three families of
PKCS

•
Goal is to provide
guidance but leave
flexibility

•
No key lengths

•
Discusses Key
Agreement, Digital
Signatures and
Encoding Schemes

•
A forum for
discussion