fulcrm_crypto/fulcrm_crypto.module

<?php

function fulcrm_crypto_permission() {
  return array( 'administer fulcrm crypto' => array( 'title' => t('Administer fulcrm cryptography'),
                                                    'description' => t('Perform main installation/administration tasks for fulcrm cryptography.'),
                                                    ),                          
                );
}

function fulcrm_crypto_menu() {
    /*
    $items[ 'admin/config/services/fulcrm' ] = array( 'page callback' => 'system_admin_menu_block_page',
                                                      'file' => 'system.admin.inc',
                                                      'file path' => drupal_get_path('module', 'system'),
                                                      'title' => 'fulcrm',
                                                      'description' => 'Configuration integration with fulcrm.org.',
                                                      'position' => 'right',
                                                      'access callback' => 'user_access',
                                                      'access arguments' => array('access administration pages'),
                                                      );
   */
    $items[ 'admin/config/services/fulcrm/crypto' ] = array( 'page callback' => 'fulcrm_crypto_admin',
                                                             'file' => 'fulcrm_crypto.admin.inc',
                                                             'title' => 'fulcrm cryptography',
                                                             'description' => 'Settings for fulcrm.org cryptography.',
                                                             'access callback' => 'user_access',
                                                             'access arguments' => array('administer fulcrm crypto'),
                                                             );

    return $items;
}

function fulcrm_crypto_object_id_hmac( $object_type, $object_id ) {
    return drupal_hmac_base64( 'fulcrm:' . strval( $object_id ) . ':' . $object_type, session_id() . drupal_get_hash_salt() );
}

function fulcrm_crypto_hash_equals( $real_hmac, $hmac ) {
    if ( function_exists( 'hash_equals' ) ) {
        return hash_equals( $real_hmac, $hmac );
    } else {
        if ( strlen( $real_hmac ) != strlen( $hmac ) )
            return false;
        $xor = $real_hmac ^ $hmac;
        $residual = 0;
        for ( $i = strlen( $xor ) - 1; $i >= 0; $i-- )
            $residual |= ord( $residual[ $i ] );
        if ( $residual == 0 )
            return true;
        return false;
    }
}

function fulcrm_crypto_check_object_id_hmac( $object_type, $object_id, $hmac ) {
    $real_hmac = fulcrm_crypto_object_id_hmac( $object_type, $object_id );
    return fulcrm_crypto_hash_equals( $real_hmac, $hmac );
}

function fulcrm_crypto_object_id_form_value( $object_type, $object_id ) {
    return $object_id . ':' . fulcrm_crypto_object_id_hmac( $object_type, $object_id );
}

function fulcrm_crypto_get_object_id_form_value( $object_type, $form_value ) {
    $bits = explode( ':', $form_value );
    if ( count( $bits ) == 2 ) {
        $object_id = $bits[ 0 ];
        $hmac = $bits[ 1 ];
        $real_hmac = fulcrm_crypto_object_id_hmac( $object_type, $object_id );

        if ( fulcrm_crypto_hash_equals( $real_hmac, $hmac ) )
            return $object_id;
    }
    return NULL;
}