Information systems slide introduction to encryption technologies

Example: Encrypted E-MailThe plaintext message is run through a hash algorithm to generate a “fingerprint”.. Example: Encrypted E-MailThe fingerprint is encrypted using Anne’s private ke

Introduction to

Encryption Technology

Mort Anvari

What is it?

- The conversion of data into a form that cannot

be easily understood by unauthorized people

- The opposite is decryption, that is, changing the difficult to read form back into the original

- It’s usually software, but can be hardware

- What does it do for me?

- Symmetric Encryption

- Asymmetric Encryption

- One Way Hash

- Example: An Encrypted E-Mail

What does it do for me?

Confidentiality: The data can only be read

by the intended recipients

Non-Repudiation: The data cannot be

forged If data is “signed” by a person, the data could only have come from

them No more “I didn’t send that!”

Data Integrity: The data cannot be

modified without detection

Symmetric Encryption

- Data is encrypted and decrypted with the same key

- Fast

- Key must be kept secret

- Key must be sent Out of Band

- DES and IDEA are symmetric

Asymmetric Encryption

- Uses 2 keys

- Data encrypted with one key can only be decrypted with the other

- Public key is shared with all

- Public key can be sent In Band

- Private key must be kept secret

- RSA is asymmetric

One Way Hash

- A “fingerprint” of data

- Any size data = same size hash

- Tiny changes in data produce

a very different hash

Example: Encrypted E-Mail

Anne wants to send e-mail to Bob The plaintext message compressed to make

it smaller and the ciphertext stronger

Plaintext

Example: Encrypted E-Mail

The plaintext message is run through a hash algorithm to generate a

“fingerprint”

Small Plaintext Hash Function Fingerprint

Example: Encrypted E-Mail

The fingerprint is encrypted using

Anne’s private key This makes it into a digital signature It is then appended to the plaintext

Anne’s Private

Key

Small Plaintext Signature Fingerprint

Example: Encrypted E-Mail

A Random key is generated and the e-mail is symmetrically encrypted using that

Small Plaintext Random Key

Ciphertext Encrypted with Random

Example: Encrypted E-Mail

The Random Key is Encrypted using Bob’s public key The result is called a

“Strong Box” Remember that only Bob can read the contents of the Box

Bob’s Public

Key

Random Key

Random Key

A Box for Bob

Random Key

A Box for Bob

Example: Encrypted E-Mail

The Box is attached to the ciphertext and they are sent over e-mail to Bob

Ciphertext

Encrypted

with

Example: Encrypted E-Mail

Bob decrypts his Strong Box to get the Random Key Only Bob’s private key

can open the Box which was encrypted with his public key

Bob’s Private

Random Key

A Box for Bob

Example: Encrypted E-Mail

Bob decrypts the ciphertext using the random key which he got from his

Strong Box

Random Key

Ciphertext

Encrypted

with Random

Small Plaintext

Example: Encrypted E-Mail

Bob decrypts Anne’s signature using her public key Since only Anne could have encrypted it with her private key, Bob knows the message had to come from her

Anne’s Public

Key

Example: Encrypted E-Mail

Bob runs the unencrypted message

through the hash function If this

fingerprint is the same as the one from the signature, the message was not

changed in transit

Small

Calculated Fingerprint

 or

Example: Encrypted E-Mail

Finally, the message is uncompressed Bob can read the message knowing for certain that it’s from Anne, it’s what

Anne wrote and only the two of them

could have read it

Plaintext