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Goals Of Cryptography

Goals Of Cryptography

Confidentiality → Authorised party can access the information

Integrity → Correctness and completeness of information

Authenticity → Source of information can be verified by the receiving party

Non-Repudiation → Source of information can be verified by any third party

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Tools For Concepts

Concept	Tool
Encryption [Confidentiality]	AES \| RSA
Cryptographic Hash Functions [Integrity]	SHA-2 \| SHA-3
Message Authentication Codes \| Authenticated Encryption [Authenticity]	HMAC and GCM block cipher mode of operation
Digital signatures [Non-Repudiation]	RSA-PSS and Ed25519

* Many more not mentioned here, this is just an example

Cryptography Goal: Confidentiality

Symmetric Encryption

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Property:

Single key K for both Encryption And Decryption

Constraint:

DEC(ENC(P,K),K)=P

In Practice:

ENC and DEC are very often the Advanced Encryption Standard (AES) block cipher
AES keys can be of length 128, 192, 256 bits
Each pair of sender and receiver needs a key and its the same key

Doesn’t scale well with the number of participants in the system

Can be used to encrypt large amount of data

NIST →

Advanced Encryption Standard (AES)

The Advanced Encryption Standard (AES) specifies a FIPS-approved cryptographic algorithm that can be used to protect electronic data.

Advanced Encryption Standard (AES)

https://www.nist.gov/publications/advanced-encryption-standard-aes

Asymmetric Encryption

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Properties:

Public Key KE to encrypt
Private Key KD to derypt

Constraint:

DEC(ENC(P,KE),KD) = P

In Practice:

Often RSA with keys ≥ 2048 bits
Requires 1 key-pair for each participant

Scales well

Size of data that can be encrypted is almost equal to the size of the key.

WIKI →

RSA (cryptosystem)

RSA (Rivest–Shamir–Adleman) is a public-key cryptosystem, one of the oldest that is widely used for secure data transmission. The acronym "RSA" comes from the surnames of Ron Rivest, Adi Shamir and Leonard Adleman, who publicly described the algorithm in 1977. An equivalent system was developed secretly in 1973 at Government Communications Headquarters (GCHQ), the British signals intelligence agency, by the English mathematician Clifford Cocks. That system was declassified in 1997.[2]

RSA (cryptosystem)

https://en.wikipedia.org/wiki/RSA_(cryptosystem)

Hybrid Encryption (Using AES and RSA)

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Sender:

Create new random symmetric key K
Send data encrypted using key K
Send key K encrypted with Receiver’s public key KE

Receiver:

Obtain symmetric key K by using Decrypting Symmetric Key using Receiver’s Private Key KD
Obtain data by decrypting data using Symmetric Key K

Main Problem:

Once KD is known all symmetric keys K can be obtained and all data can be decrypted
Can be prevented by using the ephemeral Diffie-Hellman key exchange EDH or ECDHE