digest Algorithm

The digest algorithm, also known as a hash function or message digest, is a cryptographic technique used to convert a given input or message into a fixed-size string of text, typically in the form of a hexadecimal number. This algorithm is designed to be a one-way function, meaning that it is computationally infeasible to reverse-engineer the original input from the generated hash. These algorithms are widely used in various applications, including data integrity checks, digital signatures, and password storage, to ensure the security and authenticity of the transmitted information. There are several well-known digest algorithms, such as MD5, SHA-1, and SHA-256, each with its unique properties in terms of the output size and complexity. When a message is passed through the digest algorithm, it undergoes a series of mathematical operations and transformations, eventually producing a fixed-length hash as the output. The primary objective of these algorithms is to ensure that even the slightest change in input data results in a significantly different hash output, which helps detect any tampering, corruption, or unauthorized modifications in the original data. Furthermore, the algorithm must be collision-resistant, implying that it should be highly improbable for two different inputs to generate the same hash output. Ultimately, the digest algorithm plays a crucial role in maintaining the security, privacy, and reliability of digital communications and transactions in the modern world.
// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use std::iter::repeat;

/**
 * The Digest trait specifies an interface common to digest functions, such as SHA-1 and the SHA-2
 * family of digest functions.
 */
pub trait Digest {
    /**
     * Provide message data.
     *
     * # Arguments
     *
     * * input - A vector of message data
     */
    fn input(&mut self, input: &[u8]);

    /**
     * Retrieve the digest result. This method may be called multiple times.
     *
     * # Arguments
     *
     * * out - the vector to hold the result. Must be large enough to contain output_bits().
     */
    fn result(&mut self, out: &mut [u8]);

    /**
     * Reset the digest. This method must be called after result() and before supplying more
     * data.
     */
    fn reset(&mut self);

    /**
     * Get the output size in bits.
     */
    fn output_bits(&self) -> usize;

    /**
     * Get the output size in bytes.
     */
    fn output_bytes(&self) -> usize {
        (self.output_bits() + 7) / 8
    }

    /**
     * Get the block size in bytes.
     */
    fn block_size(&self) -> usize;

    /**
     * Convenience function that feeds a string into a digest.
     *
     * # Arguments
     *
     * * `input` The string to feed into the digest
     */
    fn input_str(&mut self, input: &str) {
        self.input(input.as_bytes());
    }

    /**
     * Convenience function that retrieves the result of a digest as a
     * String in hexadecimal format.
     */
    fn result_str(&mut self) -> String {
        use serialize::hex::ToHex;

        let mut buf: Vec<u8> = repeat(0).take((self.output_bits()+7)/8).collect();
        self.result(&mut buf);
        buf[..].to_hex()
    }
}

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