BLAKE2b Hashing Context and API Prototypes

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In this tutorial, we will be discussing BLAKE2b with key for message authentication an efficient cryptographic hash function that provides both confidentiality (through encryption) and integrity (through message authentication). This feature allows for the creation of authenticated hashes, where an attacker cannot modify or tamper with original data without being detected by the verification process.

BLAKE2b is a sponge construction that combines compression functions with feedback mechanisms to provide constant-time performance and efficient parallelization. It uses variable-length output ranging from 1 byte (8 bits) to 512 bytes (64 kilobits). BLAKE2b also supports message authentication using a secret key, which is combined with the input data before being fed into the compression functions. This results in a unique output that can only be generated by an attacker who knows both the original data and the secret key.

The hash function provides strong collision resistance, meaning that it’s highly unlikely for two different inputs to produce the same output (a collision). This makes BLAKE2b ideal for use in resource-constrained environments where speed is critical. In terms of implementation, BLAKE2b can be used in conjunction with other cryptographic primitives such as symmetric encryption algorithms like AES to provide a more secure solution for data protection and integrity.

To implement message authentication using the secret key, we first need to initialize the hash function context (ctx) by calling blake2b_init(). We then pass in the desired output length (in bytes), followed by any additional parameters such as personalization strings or salt values. Next, we call blake2b(md, outlen, key, keylen, data, datalen) to perform both hashing and message authentication using the secret key. The md parameter is a pointer to an output buffer where the hash value will be stored, while outlen specifies the desired length of the output in bytes. The key and keylen parameters are used for message authentication, with key being a pointer to the secret key and keylen specifying its length in bytes. Finally, data and datalen specify the input data that we want to hash and authenticate using the secret key.

Here’s an example implementation of BLAKE2b with message authentication:

#include "blake2b.h"

// Define a personalization string for our application
const char *personal = "My Application";

int main() {
    // Initialize the hash function context using 32 bytes output length and personalization string
    blake2b_ctx ctx;
    if (blake2b_init(&ctx, 32, NULL, strlen(personal)) != 0) { //initialize the BLAKE2b hash function with 32 bytes output length and personalization string
        printf("Error: Failed to initialize BLAKE2b hash function\n"); //print error message if initialization fails
        return -1;
    }

    // Define the input data and secret key for message authentication
    const char *data = "This is some sample data"; //input data to be hashed and authenticated
    const uint8_t key[32] = { 0xDE, 0xAD, 0xBE, ... }; //secret key for message authentication, specified as a 32-byte array

    // Hash and authenticate the input data using BLAKE2b with message authentication
    size_t datalen = strlen(data); //get the length of the input data
    blake2b(ctx.hash, 32, key, sizeof(key), (const uint8_t *)data, datalen); //hash and authenticate the input data using BLAKE2b with message authentication
    blake2b_update(&ctx, ctx.hash, 32); //update the hash function context with the hashed and authenticated data

    // Finalize the hash function and store the output in a buffer
    size_t outlen = 32; //set the output length to 32 bytes
    uint8_t md[64]; //create a buffer to store the output
    if (blake2b_final(&ctx, md) != 0) { //finalize the hash function and store the output in the buffer
        printf("Error: Failed to finalize BLAKE2b hash function\n"); //print error message if finalization fails
        return -1;
    }

    // Verify the output by comparing it with a known good value
    const uint8_t expected[32] = { 0xDE, 0xEF, ... }; //known good value to compare the output with
    for (int i = 0; i < outlen; ++i) { //loop through the output buffer
        if (md[i] != expected[i]) { //compare each byte of the output with the expected value
            printf("Error: Hash output does not match the expected value\n"); //print error message if output does not match expected value
            return -1;
        }
    }

    // Clean up resources and exit gracefully
    blake2b_free(&ctx); //free the resources used by the hash function context
    return 0; //exit the program
}

In this example, we first initialize the hash function context using a personalization string. We then define the input data and secret key for message authentication, followed by hashing and authenticating the input data using BLAKE2b with message authentication. Finally, we finalize the hash function and store the output in a buffer before verifying it against a known good value.

In terms of performance, BLAKE2b provides constant-time performance due to its sponge construction, which allows for efficient parallelization. This makes it ideal for use in resource-constrained environments where speed is critical. In addition, the hash function provides strong collision resistance and message authentication using a secret key, making it an excellent choice for applications that require both confidentiality and integrity.

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