Non-repudiation - CompTIA Security+ SY0-701 - 1.2

Understanding Nonrepudiation in Cryptography

The Importance of Data Verification

• Nonrepudiation is a foundational aspect of cryptography, ensuring that data sent to a third party can be verified as coming from the original sender.

• Similar to signing a contract, cryptographic methods provide features that allow verification of the sender's identity and the integrity of the data.

Proof of Integrity

• Proof of integrity ensures that received data matches exactly what was originally sent, confirming its accuracy and consistency.

• A hash function generates a short string (hash or message digest) based on the original data, acting like a fingerprint for verification.

• If any change occurs in the data, even one character, the resulting hash will differ significantly from the original.

Practical Example: Project Gutenberg

• An example involving downloading volume one of the Gutenberg Encyclopedia illustrates how hashing works to verify data integrity.

• Changing even a single character in an 8.1 MB file results in a completely different hash value, making it easy to detect alterations.

Additional Integrity: Proof of Origin

• Beyond proof of integrity, proof of origin verifies who sent the data using digital signatures for nonrepudiation.

• Digital signatures utilize private keys known only to senders; public keys are used by recipients to confirm authenticity.

The Process Behind Digital Signatures

• When Alice sends Bob a message ("You're hired"), she first creates a hash and encrypts it with her private key before sending it along with her message.

Digital Signature Verification Process

Understanding the Decryption and Hashing Steps

• The process begins with decrypting a message using a public key, which reveals the original hash of the plaintext message. This is crucial for verifying the integrity of the received information.

• Bob will replicate Alice's initial hashing function on the original plaintext to generate a new hash. This step ensures that he can compare it against the hash included in the digital signature.

• If Bob's generated hash matches the one from Alice's digital signature, it confirms two things:

• The information received is identical to what was sent.

• The authenticity of the sender, confirming that it indeed came from Alice.

Automation of Digital Signature Processes