utils.h

//------------------------------------------------------------------------------
/*
    This file is part of rippled: https://github.com/ripple/rippled
    Copyright (c) 2016 Ripple Labs Inc.
 
    Permission to use, copy, modify, and/or distribute this software for any
    purpose  with  or without fee is hereby granted, provided that the above
    copyright notice and this permission notice appear in all copies.
 
    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
//==============================================================================
 
#ifndef RIPPLE_CONDITIONS_UTILS_H
#define RIPPLE_CONDITIONS_UTILS_H
 
#include <xrpld/conditions/detail/error.h>
 
#include <xrpl/basics/Buffer.h>
#include <xrpl/basics/Slice.h>
 
#include <boost/dynamic_bitset.hpp>
 
#include <limits>
 
namespace ripple {
namespace cryptoconditions {
 
// A collection of functions to decode binary blobs
// encoded with X.690 Distinguished Encoding Rules.
//
// This is a very trivial decoder and only implements
// the bare minimum needed to support PreimageSha256.
namespace der {
 
// The preamble encapsulates the DER identifier and
// length octets:
struct Preamble
{
    explicit Preamble() = default;
    std::uint8_t type = 0;
    std::size_t tag = 0;
    std::size_t length = 0;
};
 
inline bool
isPrimitive(Preamble const& p)
{
    return (p.type & 0x20) == 0;
}
 
inline bool
isConstructed(Preamble const& p)
{
    return !isPrimitive(p);
}
 
inline bool
isUniversal(Preamble const& p)
{
    return (p.type & 0xC0) == 0;
}
 
inline bool
isApplication(Preamble const& p)
{
    return (p.type & 0xC0) == 0x40;
}
 
inline bool
isContextSpecific(Preamble const& p)
{
    return (p.type & 0xC0) == 0x80;
}
 
inline bool
isPrivate(Preamble const& p)
{
    return (p.type & 0xC0) == 0xC0;
}
 
inline Preamble
parsePreamble(Slice& s, std::error_code& ec)
{
    Preamble p;
 
    if (s.size() < 2)
    {
        ec = error::short_preamble;
        return p;
    }
 
    p.type = s[0] & 0xE0;
    p.tag = s[0] & 0x1F;
 
    s += 1;
 
    if (p.tag == 0x1F)
    {  // Long tag form, which we do not support:
        ec = error::long_tag;
        return p;
    }
 
    p.length = s[0];
    s += 1;
 
    if (p.length & 0x80)
    {  // Long form length:
        std::size_t const cnt = p.length & 0x7F;
 
        if (cnt == 0)
        {
            ec = error::malformed_encoding;
            return p;
        }
 
        if (cnt > sizeof(std::size_t))
        {
            ec = error::large_size;
            return p;
        }
 
        if (cnt > s.size())
        {
            ec = error::short_preamble;
            return p;
        }
 
        p.length = 0;
 
        for (std::size_t i = 0; i != cnt; ++i)
            p.length = (p.length << 8) + s[i];
 
        s += cnt;
 
        if (p.length == 0)
        {
            ec = error::malformed_encoding;
            return p;
        }
    }
 
    return p;
}
 
inline Buffer
parseOctetString(Slice& s, std::uint32_t count, std::error_code& ec)
{
    if (count > s.size())
    {
        ec = error::buffer_underfull;
        return {};
    }
 
    if (count > 65535)
    {
        ec = error::large_size;
        return {};
    }
 
    Buffer b(s.data(), count);
    s += count;
    return b;
}
 
template <class Integer>
Integer
parseInteger(Slice& s, std::size_t count, std::error_code& ec)
{
    Integer v{0};
 
    if (s.empty())
    {
        // can never have zero sized integers
        ec = error::malformed_encoding;
        return v;
    }
 
    if (count > s.size())
    {
        ec = error::buffer_underfull;
        return v;
    }
 
    bool const isSigned = std::numeric_limits<Integer>::is_signed;
    // unsigned types may have a leading zero octet
    size_t const maxLength = isSigned ? sizeof(Integer) : sizeof(Integer) + 1;
    if (count > maxLength)
    {
        ec = error::large_size;
        return v;
    }
 
    if (!isSigned && (s[0] & (1 << 7)))
    {
        // trying to decode a negative number into a positive value
        ec = error::malformed_encoding;
        return v;
    }
 
    if (!isSigned && count == sizeof(Integer) + 1 && s[0])
    {
        // since integers are coded as two's complement, the first byte may
        // be zero for unsigned reps
        ec = error::malformed_encoding;
        return v;
    }
 
    v = 0;
    for (size_t i = 0; i < count; ++i)
        v = (v << 8) | (s[i] & 0xff);
 
    if (isSigned && (s[0] & (1 << 7)))
    {
        for (int i = count; i < sizeof(Integer); ++i)
            v |= (Integer(0xff) << (8 * i));
    }
    s += count;
    return v;
}
 
}  // namespace der
}  // namespace cryptoconditions
}  // namespace ripple
 
#endif