Cryptography: Ensuring Information Security in the Digital Age

Current article is an extension to my previous article. Please read it first to have more context before, moving to this article, link below.

Cryptography is the practice of securing communication from third-party interference or unauthorized access by converting it into a format that can only be understood by those who have the key to decrypt it. It involves techniques such as encryption, decryption, and digital signatures to ensure the confidentiality, integrity, and authenticity of information.

Cryptography is used in various applications such as secure communication between two parties, secure storage of sensitive information, and secure online transactions. It is essential in protecting the confidentiality and integrity of data in today's digital age.

Encryption is the process of converting plaintext (unencrypted data) into ciphertext (encrypted data) using an encryption algorithm and a secret key. The ciphertext can only be decrypted back into plaintext using the same encryption algorithm and the secret key. This process of encryption and decryption ensures that only the intended recipient can access the information.

There are two main types of encryption algorithms: symmetric encryption and asymmetric encryption.

Symmetric encryption involves using the same key for both encryption and decryption. This means that the sender and the recipient must have access to the same secret key to encrypt and decrypt the message. The most common symmetric encryption algorithms are the Advanced Encryption Standard (AES) and the Data Encryption Standard (DES).

Asymmetric encryption involves using a public key to encrypt the message and a private key to decrypt the message. The public key is freely available, but the private key is kept secret. The most common asymmetric encryption algorithm is the RSA algorithm.

The encryption process involves several steps:

1. The plaintext message is first broken down into smaller chunks called blocks.
2. The encryption algorithm takes each block and uses the secret key to transform it into a unique ciphertext block.
3. The ciphertext blocks are then combined to form the final encrypted message.

The decryption process is the reverse of the encryption process:

1. The encrypted message is broken down into ciphertext blocks.
2. The decryption algorithm uses the secret key to transform each ciphertext block back into plaintext.
3. The plaintext blocks are then combined to form the original plaintext message.

Encryption is used in various applications such as secure communication between two parties, secure storage of sensitive information, and secure online transactions. It is an essential tool in protecting the confidentiality and integrity of data in today's digital age.

The main differences between symmetric and asymmetric encryption are:

1. Key distribution: In symmetric encryption, the same secret key is used by both the sender and the recipient, and therefore, the key must be securely distributed to both parties. In asymmetric encryption, the sender encrypts the message with the recipient's public key, which can be freely distributed, and the recipient decrypts the message using their private key.
2. Speed: Symmetric encryption is faster and more efficient than asymmetric encryption because it uses a single key to encrypt and decrypt the message. Asymmetric encryption is slower and less efficient because it uses two keys for encryption and decryption.
3. Security: Asymmetric encryption is more secure than symmetric encryption because the private key is kept secret and cannot be easily accessed by unauthorized users. In symmetric encryption, the key must be shared between the sender and the recipient, making it more vulnerable to attacks.

Both symmetric and asymmetric encryption have their own strengths and weaknesses, and their use depends on the specific requirements of the application. In practice, hybrid encryption, which combines both symmetric and asymmetric encryption, is often used to provide the benefits of both types of encryption.

Hybrid encryption is a technique that combines both symmetric and asymmetric encryption to provide the benefits of both. In hybrid encryption, a random symmetric key is used to encrypt the message, and then the symmetric key is encrypted using asymmetric encryption.

The process of hybrid encryption involves the following steps:

1. The sender generates a random symmetric key for each message.
2. The sender encrypts the message using the symmetric key.
3. The sender encrypts the symmetric key using the recipient's public key.
4. The sender sends the encrypted message and the encrypted symmetric key to the recipient.
5. The recipient decrypts the encrypted symmetric key using their private key.
6. The recipient decrypts the message using the decrypted symmetric key.

The advantage of using hybrid encryption is that it provides the security of symmetric encryption with the flexibility of asymmetric encryption. The symmetric encryption provides fast encryption and decryption of the message, while the asymmetric encryption provides a secure way to exchange the symmetric key.

Hybrid encryption is commonly used in secure communication protocols such as HTTPS, which is used to secure online transactions. In HTTPS, the web server sends an encrypted message to the client using a symmetric key, and the symmetric key is encrypted using the client's public key. This ensures that the communication is secure and that the client can authenticate the server's identity.

How to share symmetric key over the internet ?

Sharing a symmetric key securely over the internet can be a challenge because symmetric encryption algorithms use the same key for encryption and decryption. Therefore, if the key falls into the wrong hands during transmission, the security of the encrypted data is compromised.

One widely used secure key exchange protocol is the Diffie-Hellman key exchange protocol.

Diffie-Hellman key exchange protocol

The Diffie-Hellman key exchange protocol uses a mathematical algorithm to allow two parties to establish a shared secret key over an insecure channel, such as the internet, without actually exchanging the key. This shared secret key can then be used for symmetric encryption.

1. The sender and receiver agree on a public prime number and a primitive root modulo of that prime number.
2. The sender generates a random secret number and computes a public key using the agreed prime number and primitive root modulo.
3. The receiver also generates a random secret number and computes a public key using the same prime number and primitive root modulo.
4. The sender and receiver exchange their public keys.
5. The sender uses their secret number and the receiver's public key to compute a shared secret key.
6. The receiver uses their secret number and the sender's public key to compute the same shared secret key.

Mode details:

1. Setup:

• Alice and Bob agree on two publicly known values: a large prime number (p) and a primitive root modulo of p (g). These values can be shared publicly without compromising the security of the protocol.
• Alice and Bob each choose a secret number, a (for Alice) and b (for Bob), which are kept secret.

2. Public Key Exchange:

• Alice computes g^a mod p, which is her public key, and sends it to Bob.
• Bob computes g^b mod p, which is his public key, and sends it to Alice.

3. Shared Secret Key Generation:

• Alice computes (g^b mod p)^a mod p, which is the shared secret key.
• Bob computes (g^a mod p)^b mod p, which is the same shared secret key.

The Diffie-Hellman key exchange protocol ensures that the shared secret key is never exchanged over the internet, making it difficult for attackers to intercept and access the key.

Other options:

1. Pre-shared key: In this approach, the sender and receiver agree upon a secret key before exchanging any messages. This key can be shared over a secure channel, such as in person or via a secure messaging platform. Once the key is agreed upon, it can be used for subsequent communication.
2. Key distribution center (KDC): A KDC is a trusted third party that is responsible for securely distributing symmetric keys to authorized parties. The KDC generates and distributes a unique key for each pair of users who wish to communicate. This approach is commonly used in Kerberos, a network authentication protocol.

Digital Signatures:

Digital signatures are a cryptographic mechanism used to provide integrity, authenticity, and non-repudiation of digital messages. Here's a detailed explanation of how digital signatures work:

Key Pair Generation:

• The signer generates a key pair consisting of a private key and a corresponding public key.
• The private key is kept secret and is used to create the digital signature.
• The public key is shared with others and is used to verify the digital signature.

Signing Process:

• The signer uses a hash function to create a fixed-length digest of the message they want to sign. The hash function ensures that any changes to the message will result in a different digest.
• The signer then uses their private key to encrypt the digest, creating the digital signature.
• The digital signature, along with the original message, is sent to the receiver.

Verification Process:

• The receiver uses the same hash function to create a digest of the original message.
• The receiver then uses the signer's public key to decrypt the digital signature, which should produce the same digest as the one created in step 2.
• If the digests match, the receiver knows that the message has not been tampered with since it was signed, and that it was signed by the owner of the private key corresponding to the public key used for verification.

Digital signatures provide several important security properties:

• Integrity: The digital signature provides a mechanism to verify that the message has not been altered or tampered with since it was signed.
• Authenticity: The digital signature provides a mechanism to verify the identity of the signer, as only the owner of the private key can create a valid signature.
• Non-repudiation: The digital signature provides evidence that the signer created and sent the message, and cannot deny it later.

Digital signatures are widely used in various applications, such as secure email, online transactions, and software updates. One common standard for digital signatures is the Digital Signature Algorithm (DSA), which is used in conjunction with the Secure Hash Algorithm (SHA) for message digest creation. Other popular digital signature schemes include the RSA algorithm and the Elliptic Curve Digital Signature Algorithm (ECDSA).

Conclusion

Cryptography plays a critical role in many areas of modern life, including online banking, e-commerce, and communication. It is also used in various applications, such as secure messaging, secure file storage, and password protection.

While cryptography provides strong protection against unauthorized access and tampering, it is not foolproof. Cryptographic systems can be vulnerable to attacks such as brute force attacks, keylogging, and side-channel attacks.

To maintain strong security, it is important to use robust encryption algorithms, securely store keys, and regularly update systems to address any known vulnerabilities.

Overall, cryptography is an essential tool for maintaining the confidentiality, integrity, and authenticity of information in today's digital age.