Cryptography Beginner Tutorial (ii) Public key cryptography RSA with one-way hash function and message authentication code

Finding discrete logarithms is very difficult

RSA is the first letter of the surname of Ron Rivest/adi Shamir/leonard Adleman.

RSA can be used for public key cryptography and digital signatures.

RSA encryption: Ciphertext = plaintext EMODN (e and N are public keys)

RSA decryption: plaintext = ciphertext DMODN (d and n are private keys)

The decryption of RSA:

Brute force: The difficulty of brute force will increase with the length of D, and when D is long enough, it is impossible to find d by brute force in real time.

Hybrid cryptography: Increase speed with a symmetric password, protect session keys with a public key password

The composition mechanism of the hybrid cipher system:

Encrypt messages with symmetric passwords

Generating the session key used in symmetric cipher encryption through pseudo-random number generators

To encrypt a session key with a public key password

Keys used to encrypt public key passwords from outside the hybrid cryptography system

One-way hash function-fingerprint

The one-way hash function is to guarantee the integrity of the message, also known as consistency.

collisions : Two different messages that produce the same hash value are called collisions.

Collision Resistance: It is difficult to find the nature of the collision is called anti-collision.

Weak collision Resistance : It is very difficult to find another message that has the same hash value as the message.

Strong collision Resistance : It is very difficult to find two different messages with the same hash value.

unidirectional : The nature of the message cannot be reversed by a hash value.

A one-way hash function, also known as a message digest function, is a digest function.

The hash value of the one-way hash function output is also known as Message Digest (MSG Digest) or fingerprint (fingerprint)

MD4 can produce a hash value of 128 bits,

The MD5 can produce a hash value of 128 bits. Strong impact resistance has been compromised, so it's not safe.

The hash value of the sha-1:160 bit, with a message limit of 264 bits, is not a problem in practice. Strong impact resistance was breached in 2005.

SHA-2 generation-sha-256:256 bits, the message limit is 264 bits, has not been breached.

SHA-2 generation-sha-384:384 bits, the message limit is 2128 bits, has not been breached.

SHA-2 generation-sha-512:512 bits, the message limit is 2128 bits, has not been breached.

Attack on one-way hash function
Brute force : attempts to crack the "weak anti-collision" attack of a one-way hash function.

Birthday Attack : This is a "strong anti-collision" attack that attempts to crack a one-way hash function.

A one-way hash function can identify "tamper", but cannot discern "camouflage".

The technologies used for authentication include message verification codes and digital signatures.

Message authentication code (mac,message authentication code)

is a technology that confirms integrity and is certified.

The input of the message authentication code includes a message of any length and a key shared between the sender and the receiver, which can output fixed-length data.

Cryptography Beginner Tutorial (ii) Public key cryptography RSA with one-way hash function and message authentication code