Info Catalog elisp: Base 64 elisp: Text elisp: Parsing HTML/XML

elisp: Checksum/Hash

 
 31.25 Checksum/Hash
 ===================
 
 Emacs has built-in support for computing “cryptographic hashes”.  A
 cryptographic hash, or “checksum”, is a digital fingerprint of a piece
 of data (e.g., a block of text) which can be used to check that you have
 an unaltered copy of that data.
 
    Emacs supports several common cryptographic hash algorithms: MD5,
 SHA-1, SHA-2, SHA-224, SHA-256, SHA-384 and SHA-512.  MD5 is the oldest
 of these algorithms, and is commonly used in “message digests” to check
 the integrity of messages transmitted over a network.  MD5 is not
 collision resistant (i.e., it is possible to deliberately design
 different pieces of data which have the same MD5 hash), so you should
 not used it for anything security-related.  A similar theoretical
 weakness also exists in SHA-1.  Therefore, for security-related
 applications you should use the other hash types, such as SHA-2.
 
  -- Function: secure-hash algorithm object &optional start end binary
      This function returns a hash for OBJECT.  The argument ALGORITHM is
      a symbol stating which hash to compute: one of ‘md5’, ‘sha1’,
      ‘sha224’, ‘sha256’, ‘sha384’ or ‘sha512’.  The argument OBJECT
      should be a buffer or a string.
 
      The optional arguments START and END are character positions
      specifying the portion of OBJECT to compute the message digest for.
      If they are ‘nil’ or omitted, the hash is computed for the whole of
      OBJECT.
 
      If the argument BINARY is omitted or ‘nil’, the function returns
      the “text form” of the hash, as an ordinary Lisp string.  If BINARY
      is non-‘nil’, it returns the hash in “binary form”, as a sequence
      of bytes stored in a unibyte string.
 
      This function does not compute the hash directly from the internal
      representation of OBJECT’s text (Text Representations).
      Instead, it encodes the text using a coding system (Coding
      Systems), and computes the hash from that encoded text.  If
      OBJECT is a buffer, the coding system used is the one which would
      be chosen by default for writing the text into a file.  If OBJECT
      is a string, the user’s preferred coding system is used (
      (emacs)Recognize Coding).
 
  -- Function: md5 object &optional start end coding-system noerror
      This function returns an MD5 hash.  It is semi-obsolete, since for
      most purposes it is equivalent to calling ‘secure-hash’ with ‘md5’
      as the ALGORITHM argument.  The OBJECT, START and END arguments
      have the same meanings as in ‘secure-hash’.
 
      If CODING-SYSTEM is non-‘nil’, it specifies a coding system to use
      to encode the text; if omitted or ‘nil’, the default coding system
      is used, like in ‘secure-hash’.
 
      Normally, ‘md5’ signals an error if the text can’t be encoded using
      the specified or chosen coding system.  However, if NOERROR is
      non-‘nil’, it silently uses ‘raw-text’ coding instead.
 

Info Catalog elisp: Base 64 elisp: Text elisp: Parsing HTML/XML