/*
 * $Id$
 * 'OpenSSL for Ruby' project
 * Copyright (C) 2001-2002  Michal Rokos <m.rokos@sh.cvut.cz>
 * All rights reserved.
 */
/*
 * This program is licenced under the same licence as Ruby.
 * (See the file 'LICENCE'.)
 */
#include "ossl.h"

#define GetDigest(obj, ctx) do { \
    Data_Get_Struct((obj), EVP_MD_CTX, (ctx)); \
    if (!(ctx)) { \
	ossl_raise(rb_eRuntimeError, "Digest CTX wasn't initialized!"); \
    } \
} while (0)
#define SafeGetDigest(obj, ctx) do { \
    OSSL_Check_Kind((obj), cDigest); \
    GetDigest((obj), (ctx)); \
} while (0)

/*
 * Classes
 */
VALUE cDigest;
VALUE eDigestError;

static VALUE ossl_digest_alloc(VALUE klass);

/*
 * Public
 */
const EVP_MD *
GetDigestPtr(VALUE obj)
{
    const EVP_MD *md;

    if (TYPE(obj) == T_STRING) {
    	const char *name = StringValueCStr(obj);

        md = EVP_get_digestbyname(name);
        if (!md)
            ossl_raise(rb_eRuntimeError, "Unsupported digest algorithm (%s).", name);
    } else {
        EVP_MD_CTX *ctx;

        SafeGetDigest(obj, ctx);

        md = EVP_MD_CTX_md(ctx);
    }

    return md;
}

VALUE
ossl_digest_new(const EVP_MD *md)
{
    VALUE ret;
    EVP_MD_CTX *ctx;

    ret = ossl_digest_alloc(cDigest);
    GetDigest(ret, ctx);
    EVP_DigestInit_ex(ctx, md, NULL);

    return ret;
}

/*
 * Private
 */
static VALUE
ossl_digest_alloc(VALUE klass)
{
    EVP_MD_CTX *ctx;
    VALUE obj;

    ctx = EVP_MD_CTX_create();
    if (ctx == NULL)
	ossl_raise(rb_eRuntimeError, "EVP_MD_CTX_create() failed");
    obj = Data_Wrap_Struct(klass, 0, EVP_MD_CTX_destroy, ctx);

    return obj;
}

VALUE ossl_digest_update(VALUE, VALUE);

/*
 *  call-seq:
 *     Digest.new(string [, data]) -> Digest
 *
 * Creates a Digest instance based on +string+, which is either the ln
 * (long name) or sn (short name) of a supported digest algorithm.
 * If +data+ (a +String+) is given, it is used as the initial input to the
 * Digest instance, i.e.
 *   digest = OpenSSL::Digest.new('sha256', 'digestdata')
 * is equal to
 *   digest = OpenSSL::Digest.new('sha256')
 *   digest.update('digestdata')
 *
 * === Example
 *   digest = OpenSSL::Digest.new('sha1')
 *
 *
 */
static VALUE
ossl_digest_initialize(int argc, VALUE *argv, VALUE self)
{
    EVP_MD_CTX *ctx;
    const EVP_MD *md;
    VALUE type, data;

    rb_scan_args(argc, argv, "11", &type, &data);
    md = GetDigestPtr(type);
    if (!NIL_P(data)) StringValue(data);

    GetDigest(self, ctx);
    EVP_DigestInit_ex(ctx, md, NULL);

    if (!NIL_P(data)) return ossl_digest_update(self, data);
    return self;
}

static VALUE
ossl_digest_copy(VALUE self, VALUE other)
{
    EVP_MD_CTX *ctx1, *ctx2;

    rb_check_frozen(self);
    if (self == other) return self;

    GetDigest(self, ctx1);
    SafeGetDigest(other, ctx2);

    if (!EVP_MD_CTX_copy(ctx1, ctx2)) {
	ossl_raise(eDigestError, NULL);
    }
    return self;
}

/*
 *  call-seq:
 *     digest.reset -> self
 *
 * Resets the Digest in the sense that any Digest#update that has been
 * performed is abandoned and the Digest is set to its initial state again.
 *
 */
static VALUE
ossl_digest_reset(VALUE self)
{
    EVP_MD_CTX *ctx;

    GetDigest(self, ctx);
    EVP_DigestInit_ex(ctx, EVP_MD_CTX_md(ctx), NULL);

    return self;
}

/*
 *  call-seq:
 *     digest.update(string) -> aString
 *
 * Not every message digest can be computed in one single pass. If a message
 * digest is to be computed from several subsequent sources, then each may
 * be passed individually to the Digest instance.
 *
 * === Example
 *   digest = OpenSSL::Digest::SHA256.new
 *   digest.update('First input')
 *   digest << 'Second input' # equivalent to digest.update('Second input')
 *   result = digest.digest
 *
 */
VALUE
ossl_digest_update(VALUE self, VALUE data)
{
    EVP_MD_CTX *ctx;

    StringValue(data);
    GetDigest(self, ctx);
    EVP_DigestUpdate(ctx, RSTRING_PTR(data), RSTRING_LEN(data));

    return self;
}

/*
 *  call-seq:
 *      digest.finish -> aString
 *
 */
static VALUE
ossl_digest_finish(int argc, VALUE *argv, VALUE self)
{
    EVP_MD_CTX *ctx;
    VALUE str;

    rb_scan_args(argc, argv, "01", &str);

    GetDigest(self, ctx);

    if (NIL_P(str)) {
        str = rb_str_new(NULL, EVP_MD_CTX_size(ctx));
    } else {
        StringValue(str);
        rb_str_resize(str, EVP_MD_CTX_size(ctx));
    }

    EVP_DigestFinal_ex(ctx, (unsigned char *)RSTRING_PTR(str), NULL);

    return str;
}

/*
 *  call-seq:
 *      digest.name -> string
 *
 * Returns the sn of this Digest instance.
 *
 * === Example
 *   digest = OpenSSL::Digest::SHA512.new
 *   puts digest.name # => SHA512
 *
 */
static VALUE
ossl_digest_name(VALUE self)
{
    EVP_MD_CTX *ctx;

    GetDigest(self, ctx);

    return rb_str_new2(EVP_MD_name(EVP_MD_CTX_md(ctx)));
}

/*
 *  call-seq:
 *      digest.digest_length -> integer
 *
 * Returns the output size of the digest, i.e. the length in bytes of the
 * final message digest result.
 *
 * === Example
 *   digest = OpenSSL::Digest::SHA1.new
 *   puts digest.digest_length # => 20
 *
 */
static VALUE
ossl_digest_size(VALUE self)
{
    EVP_MD_CTX *ctx;

    GetDigest(self, ctx);

    return INT2NUM(EVP_MD_CTX_size(ctx));
}

/*
 *  call-seq:
 *      digest.block_length -> integer
 *
 * Returns the block length of the digest algorithm, i.e. the length in bytes
 * of an individual block. Most modern partition a message to be digested into
 * a sequence of fix-sized blocks that are processed consecutively.
 *
 * === Example
 *   digest = OpenSSL::Digest::SHA1.new
 *   puts digest.block_length # => 64
 */
static VALUE
ossl_digest_block_length(VALUE self)
{
    EVP_MD_CTX *ctx;

    GetDigest(self, ctx);

    return INT2NUM(EVP_MD_CTX_block_size(ctx));
}

/*
 * INIT
 */
void
Init_ossl_digest()
{
    rb_require("digest");

#if 0
    mOSSL = rb_define_module("OpenSSL"); /* let rdoc know about mOSSL */
#endif

    /* Document-class: OpenSSL::Digest
     *
     * OpenSSL::Digest allows you to compute message digests (sometimes
     * interchangeably called "hashes") of arbitrary data that are
     * cryptographically secure, i.e. a Digest implements a secure one-way
     * function.
     *
     * One-way functions offer some useful properties. E.g. given two
     * distinct inputs the probability that both yield the same output
     * is highly unlikely. Combined with the fact that every message digest
     * algorithm has a fixed-length output of just a few bytes, digests are
     * often used to create unique identifiers for arbitrary data. A common
     * example is the creation of a unique id for binary documents that are
     * stored in a database.
     *
     * Another useful characteristic of one-way functions (and thus the name)
     * is that given a digest there is no indication about the original
     * data that produced it, i.e. the only way to identify the original input
     * is to "brute-force" through every possible combination of inputs.
     *
     * These characteristics make one-way functions also ideal companions
     * for public key signature algorithms: instead of signing an entire
     * document, first a hash of the document is produced with a considerably
     * faster message digest algorithm and only the few bytes of its output
     * need to be signed using the slower public key algorithm. To validate
     * the integrity of a signed document, it suffices to re-compute the hash
     * and verify that it is equal to that in the signature.
     *
     * Among the supported message digest algorithms are:
     * * SHA, SHA1, SHA224, SHA256, SHA384 and SHA512
     * * MD2, MD4, MDC2 and MD5
     * * RIPEMD160
     * * DSS, DSS1 (Pseudo algorithms to be used for DSA signatures. DSS is
     *   equal to SHA and DSS1 is equal to SHA1)
     *
     * For each of these algorithms, there is a sub-class of Digest that
     * can be instantiated as simply as e.g.
     *
     *   digest = OpenSSL::Digest::SHA1.new
     *
     * === Mapping between Digest class and sn/ln
     *
     * The sn (short names) and ln (long names) are defined in
     * <openssl/object.h> and <openssl/obj_mac.h>. They are textual
     * representations of ASN.1 OBJECT IDENTIFIERs. Each supported digest
     * algorithm has an OBJECT IDENTIFIER associated to it and those again
     * have short/long names assigned to them.
     * E.g. the OBJECT IDENTIFIER for SHA-1 is 1.3.14.3.2.26 and its
     * sn is "SHA1" and its ln is "sha1".
     * ==== MD2
     * * sn: MD2
     * * ln: md2
     * ==== MD4
     * * sn: MD4
     * * ln: md4
     * ==== MD5
     * * sn: MD5
     * * ln: md5
     * ==== SHA
     * * sn: SHA
     * * ln: SHA
     * ==== SHA-1
     * * sn: SHA1
     * * ln: sha1
     * ==== SHA-224
     * * sn: SHA224
     * * ln: sha224
     * ==== SHA-256
     * * sn: SHA256
     * * ln: sha256
     * ==== SHA-384
     * * sn: SHA384
     * * ln: sha384
     * ==== SHA-512
     * * sn: SHA512
     * * ln: sha512
     *
     * "Breaking" a message digest algorithm means defying its one-way
     * function characteristics, i.e. producing a collision or finding a way
     * to get to the original data by means that are more efficient than
     * brute-forcing etc. Most of the supported digest algorithms can be
     * considered broken in this sense, even the very popular MD5 and SHA1
     * algorithms. Should security be your highest concern, then you should
     * probably rely on SHA224, SHA256, SHA384 or SHA512.
     *
     * === Hashing a file
     *
     *   data = File.read('document')
     *   sha256 = OpenSSL::Digest::SHA256.new
     *   digest = sha256.digest(data)
     *
     * === Hashing several pieces of data at once
     *
     *   data1 = File.read('file1')
     *   data2 = File.read('file2')
     *   data3 = File.read('file3')
     *   sha256 = OpenSSL::Digest::SHA256.new
     *   sha256 << data1
     *   sha256 << data2
     *   sha256 << data3
     *   digest = sha256.digest
     */
    cDigest = rb_define_class_under(mOSSL, "Digest", rb_path2class("Digest::Class"));
    /* Document-class: OpenSSL::Digest::DigestError
     *
     * Generic Exception class that is raised if an error occurs during a
     * Digest operation.
     */
    eDigestError = rb_define_class_under(cDigest, "DigestError", eOSSLError);

    rb_define_alloc_func(cDigest, ossl_digest_alloc);

    rb_define_method(cDigest, "initialize", ossl_digest_initialize, -1);
    rb_define_copy_func(cDigest, ossl_digest_copy);
    rb_define_method(cDigest, "reset", ossl_digest_reset, 0);
    rb_define_method(cDigest, "update", ossl_digest_update, 1);
    rb_define_alias(cDigest, "<<", "update");
    rb_define_private_method(cDigest, "finish", ossl_digest_finish, -1);
    rb_define_method(cDigest, "digest_length", ossl_digest_size, 0);
    rb_define_method(cDigest, "block_length", ossl_digest_block_length, 0);

    rb_define_method(cDigest, "name", ossl_digest_name, 0);
}