Cryptography Tutorials - Herong's Tutorial Examples - v5.42, by Herong Yang
Illustration of RSA Algorithm: p,q=5,7
This section provides a tutorial example to illustrate how RSA public key encryption algorithm works with 2 small prime numbers 5 and 7.
To demonstrate the RSA public key encryption algorithm, let's start it with 2 smaller prime numbers 5 and 7.
Generation the public key and private key with prime numbers of 5 and 7 can be illustrated as:
Given p as 5
Given q as 7
Compute n = p*q: n = 5*7 = 35
Compute m = (p-1)*(q-1): m = 4*6 = 24
Select e, such that e and m are coprime numbers: e = 5
Compute d, such that d*e mod m = 1: d = 29
The public key {n,e} is = {35,5}
The private key {n,d} is = {35,29}
With the public key of {35,5}, encryption of a cleartext M represented as number 23 can be illustrated as:
Given public key {n,e} as {35,5}
Given cleartext M represented in number as 23
Divide B into blocks: 1 block is enough
Compute encrypted block C = M**e mod n:
C = 23**5 mod 35 = 6436343 mod 35 = 18
The ciphertext C represented in number is 18
With the private key of {35,29}, decryption of the ciphertext C represented as number 18 can be illustrated as:
Given private key {n,e} as {35,29}
Given ciphertext C represented in number as 18
Divide C into blocks: 1 block is enough
Compute encrypted block M = C**d mod n:
M = 18**29 mod 35
= 18*18**28 mod 35
= 18*(18**4)**7 mod 35
= 18*(104976)**7 mode 35
= 18*(104976 mod 35)**7 mod 35
= 18*(11)**7 mod 35
= 18*19487171 mod 35
= 350769078 mod 35
= 23
The cleartext M represented in number is 23
Cool. RSA public key encryption algorithm works. We are getting the original cleartext 23 back using the decryption algorithm and private key!
Notice that I had to compute "18**29 mod 35" in multiple steps, because 18**29 is too big to be computed directly.
Table of Contents
Introduction to AES (Advanced Encryption Standard)
DES Algorithm - Illustrated with Java Programs
DES Algorithm Java Implementation
DES Algorithm - Java Implementation in JDK JCE
DES Encryption Operation Modes
PHP Implementation of DES - mcrypt
Blowfish - 8-Byte Block Cipher
Secret Key Generation and Management
Cipher - Secret Key Encryption and Decryption
►Introduction of RSA Algorithm
What Is Public Key Encryption?
RSA Public Key Encryption Algorithm
►Illustration of RSA Algorithm: p,q=5,7
Illustration of RSA Algorithm: p,q=7,19
Proof of RSA Public Key Encryption
Efficient RSA Encryption and Decryption Operations
Proof of RSA Encryption Operation Algorithm
RSA Implementation using java.math.BigInteger Class
Introduction of DSA (Digital Signature Algorithm)
Java Default Implementation of DSA
Private key and Public Key Pair Generation
PKCS#8/X.509 Private/Public Encoding Standards
Cipher - Public Key Encryption and Decryption
OpenSSL Introduction and Installation
OpenSSL Generating and Managing RSA Keys
OpenSSL Generating and Signing CSR
OpenSSL Validating Certificate Path
"keytool" and "keystore" from JDK
"OpenSSL" Signing CSR Generated by "keytool"
Migrating Keys from "keystore" to "OpenSSL" Key Files
Certificate X.509 Standard and DER/PEM Formats
Migrating Keys from "OpenSSL" Key Files to "keystore"