der_enc.cpp

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/*
* DER Encoder
* (C) 1999-2007,2018 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#include <botan/der_enc.h>
 
#include <botan/asn1_obj.h>
#include <botan/bigint.h>
#include <botan/internal/asn1_utils.h>
#include <botan/internal/bit_ops.h>
#include <botan/internal/fmt.h>
#include <botan/internal/loadstor.h>
#include <botan/internal/mem_utils.h>
#include <algorithm>
 
namespace Botan {
 
namespace {
 
/*
* DER encode an ASN.1 type tag
*/
void encode_tag(std::vector<uint8_t>& encoded_tag, ASN1_Type type_tag_e, ASN1_Class class_tag_e) {
   const uint32_t type_tag = static_cast<uint32_t>(type_tag_e);
   const uint32_t class_tag = static_cast<uint32_t>(class_tag_e);
 
   if((class_tag | 0xE0) != 0xE0) {
      throw Encoding_Error(fmt("DER_Encoder: Invalid class tag {}", std::to_string(class_tag)));
   }
 
   if(type_tag <= 30) {
      encoded_tag.push_back(static_cast<uint8_t>(type_tag | class_tag));
   } else {
      size_t blocks = high_bit(static_cast<uint32_t>(type_tag)) + 6;
      blocks = (blocks - (blocks % 7)) / 7;
 
      BOTAN_ASSERT_NOMSG(blocks > 0);
 
      encoded_tag.push_back(static_cast<uint8_t>(class_tag | 0x1F));
      for(size_t i = 0; i != blocks - 1; ++i) {
         encoded_tag.push_back(0x80 | ((type_tag >> 7 * (blocks - i - 1)) & 0x7F));
      }
      encoded_tag.push_back(type_tag & 0x7F);
   }
}
 
/*
* DER encode an ASN.1 length field
*/
void encode_length(std::vector<uint8_t>& encoded_length, size_t length) {
   if(length <= 127) {
      encoded_length.push_back(static_cast<uint8_t>(length));
   } else {
      const size_t bytes_needed = significant_bytes(length);
 
      encoded_length.push_back(static_cast<uint8_t>(0x80 | bytes_needed));
 
      for(size_t i = sizeof(length) - bytes_needed; i < sizeof(length); ++i) {
         encoded_length.push_back(get_byte_var(i, length));
      }
   }
}
 
}  // namespace
 
namespace ASN1 {
 
std::vector<uint8_t> der_sequence_header(size_t contents_len) {
   std::vector<uint8_t> header;
   header.reserve(2 + sizeof(contents_len));
   encode_tag(header, ASN1_Type::Sequence, ASN1_Class::Constructed);
   encode_length(header, contents_len);
   return header;
}
 
}  // namespace ASN1
 
DER_Encoder::DER_Encoder(secure_vector<uint8_t>& vec) {
   m_append_output = [&vec](const uint8_t b[], size_t l) {
      if(l > 0) {
         vec.insert(vec.end(), b, b + l);
      }
   };
}
 
DER_Encoder::DER_Encoder(std::vector<uint8_t>& vec) {
   m_append_output = [&vec](const uint8_t b[], size_t l) {
      if(l > 0) {
         vec.insert(vec.end(), b, b + l);
      }
   };
}
 
/*
* Push the encoded SEQUENCE/SET to the encoder stream
*/
void DER_Encoder::DER_Sequence::push_contents(DER_Encoder& der) {
   const auto real_class_tag = m_class_tag | ASN1_Class::Constructed;
 
   if(m_sort_contents) {
      std::sort(m_set_contents.begin(), m_set_contents.end());
      for(const auto& set_elem : m_set_contents) {
         m_contents += set_elem;
      }
      m_set_contents.clear();
   }
 
   der.add_object(m_type_tag, real_class_tag, m_contents.data(), m_contents.size());
   m_contents.clear();
}
 
/*
* Add an encoded value to the SEQUENCE/SET
*/
void DER_Encoder::DER_Sequence::add_bytes(const uint8_t data[], size_t length) {
   if(m_sort_contents) {
      if(length > 0) {
         m_set_contents.emplace_back(data, data + length);
      } else {
         m_set_contents.emplace_back();
      }
   } else {
      m_contents += std::make_pair(data, length);
   }
}
 
void DER_Encoder::DER_Sequence::add_bytes(const uint8_t hdr[], size_t hdr_len, const uint8_t val[], size_t val_len) {
   if(m_sort_contents) {
      secure_vector<uint8_t> m;
      m.reserve(hdr_len + val_len);
      m += std::make_pair(hdr, hdr_len);
      m += std::make_pair(val, val_len);
      m_set_contents.push_back(std::move(m));
   } else {
      m_contents += std::make_pair(hdr, hdr_len);
      m_contents += std::make_pair(val, val_len);
   }
}
 
/*
* Return the type and class taggings
*/
uint32_t DER_Encoder::DER_Sequence::tag_of() const {
   return m_type_tag | m_class_tag;
}
 
/*
* DER_Sequence Constructor
*/
DER_Encoder::DER_Sequence::DER_Sequence(ASN1_Type type_tag, ASN1_Class class_tag, bool sort_contents) :
      m_type_tag(type_tag),
      m_class_tag(class_tag),
      m_sort_contents(sort_contents || (type_tag == ASN1_Type::Set && class_tag == ASN1_Class::Universal)) {}
 
/*
* Return the encoded contents
*/
secure_vector<uint8_t> DER_Encoder::get_contents() {
   if(!m_subsequences.empty()) {
      throw Invalid_State("DER_Encoder: Sequence hasn't been marked done");
   }
 
   if(m_append_output) {
      throw Invalid_State("DER_Encoder Cannot get contents when using output vector");
   }
 
   secure_vector<uint8_t> output;
   std::swap(output, m_default_outbuf);
   return output;
}
 
std::vector<uint8_t> DER_Encoder::get_contents_unlocked() {
   if(!m_subsequences.empty()) {
      throw Invalid_State("DER_Encoder: Sequence hasn't been marked done");
   }
 
   if(m_append_output) {
      throw Invalid_State("DER_Encoder Cannot get contents when using output vector");
   }
 
   std::vector<uint8_t> output(m_default_outbuf.begin(), m_default_outbuf.end());
   m_default_outbuf.clear();
   return output;
}
 
/*
* Start a new ASN.1 SEQUENCE/SET/EXPLICIT
*/
DER_Encoder& DER_Encoder::start_cons(ASN1_Type type_tag, ASN1_Class class_tag) {
   return start_cons(type_tag, class_tag, false);
}
 
DER_Encoder& DER_Encoder::start_set(ASN1_Type type_tag, ASN1_Class class_tag) {
   return start_cons(type_tag, class_tag, true);
}
 
DER_Encoder& DER_Encoder::start_cons(ASN1_Type type_tag, ASN1_Class class_tag, bool sort_contents) {
   m_subsequences.push_back(DER_Sequence(type_tag, class_tag, sort_contents));
   return (*this);
}
 
/*
* Finish the current ASN.1 SEQUENCE/SET/EXPLICIT
*/
DER_Encoder& DER_Encoder::end_cons() {
   if(m_subsequences.empty()) {
      throw Invalid_State("DER_Encoder::end_cons: No such sequence");
   }
 
   DER_Sequence last_seq = std::move(m_subsequences[m_subsequences.size() - 1]);
   m_subsequences.pop_back();
   last_seq.push_contents(*this);
 
   return (*this);
}
 
/*
* Start a new ASN.1 EXPLICIT encoding
*/
DER_Encoder& DER_Encoder::start_explicit(uint16_t type_no) {
   return start_cons(static_cast<ASN1_Type>(type_no), ASN1_Class::ContextSpecific);
}
 
/*
* Finish the current ASN.1 EXPLICIT encoding
*/
DER_Encoder& DER_Encoder::end_explicit() {
   return end_cons();
}
 
/*
* Write raw bytes into the stream
*/
DER_Encoder& DER_Encoder::raw_bytes(const uint8_t bytes[], size_t length) {
   if(!m_subsequences.empty()) {
      m_subsequences[m_subsequences.size() - 1].add_bytes(bytes, length);
   } else if(m_append_output) {
      m_append_output(bytes, length);
   } else {
      m_default_outbuf += std::make_pair(bytes, length);
   }
 
   return (*this);
}
 
DER_Encoder& DER_Encoder::add_object_tlv(ASN1_Type type_tag, ASN1_Class class_tag, std::vector<uint8_t> tlv) {
   // `tlv` was just produced by us via DER_Encoder, so it's a single
   // well-formed TLV. Skip over the tag and length bytes (without
   // reinterpreting them) to find the body offset.
   BOTAN_ASSERT_NOMSG(!tlv.empty());
   class_tag =
      static_cast<ASN1_Class>(static_cast<uint32_t>(class_tag) & ~static_cast<uint32_t>(ASN1_Class::Constructed));
   if((tlv[0] & static_cast<uint8_t>(ASN1_Class::Constructed)) != 0) {
      class_tag = class_tag | ASN1_Class::Constructed;
   }
 
   size_t off = 1;
   // Multi-byte tag form (X.690 8.1.2.4): low 5 bits set to 0x1F, then
   // continuation bytes whose MSB is 1 except the last.
   if((tlv[0] & 0x1F) == 0x1F) {
      while(off < tlv.size() && (tlv[off] & 0x80) != 0) {
         ++off;
      }
      BOTAN_ASSERT_NOMSG(off < tlv.size());
      ++off;
   }
   // Length: short form is one byte; long form (MSB set) names the
   // number of length-of-length bytes that follow.
   BOTAN_ASSERT_NOMSG(off < tlv.size());
   const uint8_t len_byte = tlv[off++];
   if((len_byte & 0x80) != 0) {
      off += (len_byte & 0x7F);
   }
   BOTAN_ASSERT_NOMSG(off <= tlv.size());
 
   return add_object(type_tag, class_tag, std::span<const uint8_t>(tlv).subspan(off));
}
 
/*
* Write the encoding of the byte(s)
*/
DER_Encoder& DER_Encoder::add_object(ASN1_Type type_tag, ASN1_Class class_tag, const uint8_t rep[], size_t length) {
   std::vector<uint8_t> hdr;
   encode_tag(hdr, type_tag, class_tag);
   encode_length(hdr, length);
 
   if(!m_subsequences.empty()) {
      m_subsequences[m_subsequences.size() - 1].add_bytes(hdr.data(), hdr.size(), rep, length);
   } else if(m_append_output) {
      m_append_output(hdr.data(), hdr.size());
      m_append_output(rep, length);
   } else {
      m_default_outbuf += hdr;
      m_default_outbuf += std::make_pair(rep, length);
   }
 
   return (*this);
}
 
/*
* Encode a NULL object
*/
DER_Encoder& DER_Encoder::encode_null() {
   return add_object(ASN1_Type::Null, ASN1_Class::Universal, nullptr, 0);
}
 
/*
* DER encode a BOOLEAN
*/
DER_Encoder& DER_Encoder::encode(bool is_true) {
   return encode(is_true, ASN1_Type::Boolean, ASN1_Class::Universal);
}
 
/*
* DER encode a small INTEGER
*/
DER_Encoder& DER_Encoder::encode(size_t n) {
   return encode(BigInt::from_u64(n), ASN1_Type::Integer, ASN1_Class::Universal);
}
 
/*
* DER encode a small INTEGER
*/
DER_Encoder& DER_Encoder::encode(const BigInt& n) {
   return encode(n, ASN1_Type::Integer, ASN1_Class::Universal);
}
 
/*
* Encode this object
*/
DER_Encoder& DER_Encoder::encode(std::span<const uint8_t> bytes, ASN1_Type real_type) {
   return encode(bytes, real_type, real_type, ASN1_Class::Universal);
}
 
/*
* DER encode a BOOLEAN
*/
DER_Encoder& DER_Encoder::encode(bool is_true, ASN1_Type type_tag, ASN1_Class class_tag) {
   const uint8_t val = is_true ? 0xFF : 0x00;
   return add_object(type_tag, class_tag, &val, 1);
}
 
/*
* DER encode a small INTEGER
*/
DER_Encoder& DER_Encoder::encode(size_t n, ASN1_Type type_tag, ASN1_Class class_tag) {
   return encode(BigInt::from_u64(n), type_tag, class_tag);
}
 
/*
* DER encode an INTEGER
*/
std::vector<uint8_t> ASN1::integer_contents(const BigInt& n) {
   if(n == 0) {
      return {0x00};
   }
 
   // Serialize magnitude with one extra leading byte
   auto contents = n.serialize(n.bytes() + 1);
 
   if(n.signum() < 0) {
      // Two's complement: bitwise NOT then increment
      for(auto& byte : contents) {
         byte = ~byte;
      }
      for(size_t i = contents.size(); i > 0; --i) {
         if(++contents[i - 1] != 0) {
            break;
         }
      }
   }
 
   /*
   * DER requires the leading byte be emitted only if it required
   */
   BOTAN_ASSERT_NOMSG(contents.size() >= 2);
   const bool leading_byte_redundant =
      (contents[0] == 0x00 && (contents[1] & 0x80) == 0) || (contents[0] == 0xFF && (contents[1] & 0x80) != 0);
 
   if(leading_byte_redundant) {
      contents.erase(contents.begin());
   }
   return contents;
}
 
DER_Encoder& DER_Encoder::encode(const BigInt& n, ASN1_Type type_tag, ASN1_Class class_tag) {
   return add_object(type_tag, class_tag, ASN1::integer_contents(n));
}
 
/*
* DER encode an OCTET STRING or BIT STRING
*/
DER_Encoder& DER_Encoder::encode(std::span<const uint8_t> bytes,
                                 ASN1_Type real_type,
                                 ASN1_Type type_tag,
                                 ASN1_Class class_tag) {
   if(real_type != ASN1_Type::OctetString && real_type != ASN1_Type::BitString) {
      throw Invalid_Argument("DER_Encoder: Invalid tag for byte/bit string");
   }
 
   if(real_type == ASN1_Type::BitString) {
      return encode_bitstring(bytes, 0, type_tag, class_tag);
   } else {
      return add_object(type_tag, class_tag, bytes);
   }
}
 
DER_Encoder& DER_Encoder::encode_bitstring(std::span<const uint8_t> bits,
                                           size_t unused_bits,
                                           ASN1_Type type_tag,
                                           ASN1_Class class_tag) {
   if(unused_bits >= 8) {
      throw Invalid_Argument("DER_Encoder: Invalid unused bit count for BIT STRING");
   }
 
   if(bits.empty() && unused_bits != 0) {
      throw Invalid_Argument("DER_Encoder: Empty BIT STRING cannot have unused bits");
   }
 
   if(unused_bits > 0 && (bits.back() & ((1U << unused_bits) - 1)) != 0) {
      throw Invalid_Argument("DER_Encoder: BIT STRING unused bits must be zero");
   }
 
   secure_vector<uint8_t> encoded;
   encoded.reserve(1 + bits.size());
   encoded.push_back(static_cast<uint8_t>(unused_bits));
   encoded.insert(encoded.end(), bits.begin(), bits.end());
   return add_object(type_tag, class_tag, encoded);
}
 
DER_Encoder& DER_Encoder::encode_bitstring(const ASN1_BitString& bits, ASN1_Type type_tag, ASN1_Class class_tag) {
   return encode_bitstring(bits.bytes(), bits.unused_bits(), type_tag, class_tag);
}
 
DER_Encoder& DER_Encoder::encode_named_bitstring(uint64_t bits,
                                                 size_t width,
                                                 ASN1_Type type_tag,
                                                 ASN1_Class class_tag) {
   if(width > 64) {
      throw Invalid_Argument("DER_Encoder: Named BIT STRING width is too large");
   }
 
   if(width < 64 && (bits >> width) != 0) {
      throw Invalid_Argument("DER_Encoder: Named BIT STRING has bits outside range");
   }
 
   if(bits == 0) {
      return encode_bitstring({}, 0, type_tag, class_tag);
   }
 
   const size_t bit_length = width - ctz(bits);
   const size_t byte_length = (bit_length + 7) / 8;
   std::vector<uint8_t> encoded(byte_length);
 
   for(size_t bit = 0; bit != bit_length; ++bit) {
      if((bits & (uint64_t(1) << (width - 1 - bit))) != 0) {
         encoded[bit / 8] |= static_cast<uint8_t>(0x80 >> (bit % 8));
      }
   }
 
   return encode_bitstring(encoded, byte_length * 8 - bit_length, type_tag, class_tag);
}
 
DER_Encoder& DER_Encoder::encode(const ASN1_Object& obj) {
   obj.encode_into(*this);
   return (*this);
}
 
/*
* Write the encoding of the byte(s)
*/
DER_Encoder& DER_Encoder::add_object(ASN1_Type type_tag, ASN1_Class class_tag, std::string_view rep_str) {
   return add_object(type_tag, class_tag, as_span_of_bytes(rep_str));
}
 
/*
* Write the encoding of the byte
*/
DER_Encoder& DER_Encoder::add_object(ASN1_Type type_tag, ASN1_Class class_tag, uint8_t rep) {
   return add_object(type_tag, class_tag, std::span<const uint8_t>{&rep, 1});
}
 
}  // namespace Botan