Have you ever wondered how websites like your bank can securely transmit your personal information online? Or how smartphone payment apps instantly authorize transactions? The secret lies in public key cryptography – an ingenious encryption method that powers much of our digital world.
When you login to a secure website or approve an e-payment, your data gets instantly scrambled and only your device can unscramble it. This protects the information flowing between you and the remote server. Public key cryptography enables this seamless encryption, even when communicating for the first time.
The Need for Asymmetric Encryption
Before the 1970s, encryption relied on symmetric cryptography – where the sender and receiver secure messages using the same private key. But safely exchanging matching keys was problematic. Any third-party could intercept and read communications unless keys were delivered in person or by courier!
In 1976, Whitfield Diffie, Martin Hellman and Ralph Merkle cracked this key exchange dilemma with asymmetric cryptography. This employs a pair of mathematically-linked encryption keys – a public key to encrypt and private key to decrypt.
The tables below show the key differences between symmetric and asymmetric cryptography:
| Symmetric Cryptography | Asymmetric Cryptography |
|---|---|
| Uses single private key | Uses public and private key pair |
| Identical keys for encryption and decryption | Different keys for encryption and decryption |
| Key distribution is challenging | Only private key must be kept secret |
| Vulnerable to third-party attacks | Enables secure digital communication between untrusted parties |
This asymmetric approach eliminated the secure key delivery issue holding back scalable encryption. Read on to discover exactly how this works!
How Public Key Cryptography Works
Public key cryptography‘s brilliance lies in the mathematically-linked key pair:
A visual representation of how public key cryptography functions
The public key encrypts data while the private key decrypts data. Surprisingly, these keys are asymmetric – knowing the public key reveals virtually nothing about the private key!
This one-way relationship enables widespread public key distribution without compromising security. Only the private key holder can decrypt messages locked by the related public key.
Here is the step-by-step process in action:
Key Generation – Alice‘s device creates an algorithmically-matched public and private key pair.
Distribution – Alice freely distributes copies of her public key as needed. She never reveals or shares her private key – it remains closely guarded on her device.
Encryption – When Bob needs to send Alice a secure message, he encrypts the data using Alice‘s freely available public key.
Decryption – The encrypted message can only be decrypted and read by Alice using her private key. Not even Bob can decipher the message he sent her!
This groundbreaking discovery opened the door to previously impossible cryptography capabilities.
Public Key Cryptography Innovations
Asymmetric encryption has catalyzed technologies transforming communication, transactions and identity:
Secure Web Browsing – SSL/TLS protocols encrypt data between browsers and servers using certificate-based public keys to enable secure websites. No more eavesdropping!
Email Encryption – OpenPGP email encryption utilizes public key cryptography so only intended recipients can decrypt messages using their private key.
Cryptocurrencies – Public keys enable safe cryptocurrency transactions and wallet balances without revealing user identities. Private keys authorize transfers through digital signatures.
Authentication – Code and document signing via private keys combined with public key validation provides authenticity not possible previously.
| Application | Public Key Use | Private Key Use |
|---|---|---|
| Secure Web Browsing | Encrypt session data | Decrypt session data |
| Email Encryption | Encrypt email content | Decrypt email content |
| Cryptocurrencies | Share public wallet address | Digitally sign transactions |
| Authentication | Validate signed data origin | Digitally sign documents |
This table summarizes how several groundbreaking technologies apply public key cryptography‘s powers.
Algorithms Powering Public Key Encryption
Various mathematical algorithms generate the public/private key pairs and encrypt/decrypt data communications:
RSA
The Rivest–Shamir–Adleman (RSA) algorithm published in 1977 remains the most widely adopted public key crypto scheme. It utilizes multiplicative groups combined with modular arithmetic as the "one-way trapdoor" function. RSA provides robust security for encryption key lengths from 2048+ bits, however performance suffers from slower speeds.
Diffie-Hellman
Diffie-Hellman enables exchanging a shared secret key between two parties communicating over an unsecured channel. Very useful for securely establishing a symmetric encryption key for continued communications. Its math is based on the discrete logarithm problem plus finite field arithmetic. Diffie-Hellman key exchange offers high speeds and forward secrecy.
Elliptic Curve
Elliptic curve cryptography (ECC) utilizes points on an elliptic curve plotted on an x and y axis as the starting point for encryption keys. The discrete logarithm of the elliptic curve produces highly secure public keys from much smaller data parameters. Leading companies use ECC in Bitcoin, WhatsApp end-to-end encryption and Apple Pay tokenization.
An elliptic curve plotted on an x and y axis underlies the encryption
How Keys Get Generated
Public key generation boils down to complex mathematical computations:
- Select two very large random prime numbers (several hundred digits long)
- Choose a mathematical relationship between the primes defined by the algorithm
- Further multiply the numbers by each other with inputs changing every round
- Additional scrambling produces the linked public and private keys
The computational intensity creates intricately connected ones and zeros – seemingly random without the hidden mathematical structure allowing decryption.
Common Cryptography Questions
Let‘s clarify some common public key cryptography questions:
Which key encrypts and which key decrypts in public key cryptography?
The publicly shared key (public key) encrypts the data while the privately held key (private key) is the only key capable of decrypting the data.
What stops someone pretending to be me online?
Digital signatures prevent identity impersonation by requiring the signature creator‘s private key to generate but allowing anyone to validate the signature using the signer‘s public key. Valid signatures prove sole access to the matching private key.
How are private keys kept secure?
Private key security boils down to properly managing secrets – treating private keys with the same care as a banking pin number or crypto wallet seed phrase. Most devices now include dedicated security chips (TPM) to isolate keys from external access.
Conclusion
Public key cryptography delivered the holy grail of encryption – enabling two untrusted parties to reliably communicate privately over insecure channels with no prior contact. Asymmetric encryption powered decades of digital communication advances since Diffie and Hellman‘s discovery.
Future cryptography work continues maximizing algorithm speed and security to propel new generations of innovations utilizing public key cryptography‘s capabilities. I hope this guide gave you an appreciation for how public keys power so much of our modern digital world! Let me know if you have any other crypto questions.
