crypto/base64/base64.cc

// Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include <openssl/base64.h>

#include <assert.h>
#include <limits.h>
#include <string.h>

#include "../internal.h"


// constant_time_lt_args_8 behaves like |constant_time_lt_8| but takes |uint8_t|
// arguments for a slightly simpler implementation.
static inline uint8_t constant_time_lt_args_8(uint8_t a, uint8_t b) {
  crypto_word_t aw = a;
  crypto_word_t bw = b;
  // |crypto_word_t| is larger than |uint8_t|, so |aw| and |bw| have the same
  // MSB. |aw| < |bw| iff MSB(|aw| - |bw|) is 1.
  return constant_time_msb_w(aw - bw);
}

// constant_time_in_range_8 returns |CONSTTIME_TRUE_8| if |min| <= |a| <= |max|
// and |CONSTTIME_FALSE_8| otherwise.
static inline uint8_t constant_time_in_range_8(uint8_t a, uint8_t min,
                                               uint8_t max) {
  a -= min;
  return constant_time_lt_args_8(a, max - min + 1);
}

// Encoding.

static uint8_t conv_bin2ascii(uint8_t a) {
  // Since PEM is sometimes used to carry private keys, we encode base64 data
  // itself in constant-time.
  a &= 0x3f;
  uint8_t ret = constant_time_select_8(constant_time_eq_8(a, 62), '+', '/');
  ret =
      constant_time_select_8(constant_time_lt_args_8(a, 62), a - 52 + '0', ret);
  ret =
      constant_time_select_8(constant_time_lt_args_8(a, 52), a - 26 + 'a', ret);
  ret = constant_time_select_8(constant_time_lt_args_8(a, 26), a + 'A', ret);
  return ret;
}

static_assert(sizeof(((EVP_ENCODE_CTX *)(NULL))->data) % 3 == 0,
              "data length must be a multiple of base64 chunk size");

int EVP_EncodedLength(size_t *out_len, size_t len) {
  if (len + 2 < len) {
    return 0;
  }
  len += 2;
  len /= 3;

  if (((len << 2) >> 2) != len) {
    return 0;
  }
  len <<= 2;

  if (len + 1 < len) {
    return 0;
  }
  len++;

  *out_len = len;
  return 1;
}

EVP_ENCODE_CTX *EVP_ENCODE_CTX_new(void) {
  return reinterpret_cast<EVP_ENCODE_CTX *>(
      OPENSSL_zalloc(sizeof(EVP_ENCODE_CTX)));
}

void EVP_ENCODE_CTX_free(EVP_ENCODE_CTX *ctx) { OPENSSL_free(ctx); }

void EVP_EncodeInit(EVP_ENCODE_CTX *ctx) {
  OPENSSL_memset(ctx, 0, sizeof(EVP_ENCODE_CTX));
}

void EVP_EncodeUpdate(EVP_ENCODE_CTX *ctx, uint8_t *out, int *out_len,
                      const uint8_t *in, size_t in_len) {
  size_t total = 0;

  *out_len = 0;
  if (in_len == 0) {
    return;
  }

  assert(ctx->data_used < sizeof(ctx->data));

  if (sizeof(ctx->data) - ctx->data_used > in_len) {
    OPENSSL_memcpy(&ctx->data[ctx->data_used], in, in_len);
    ctx->data_used += (unsigned)in_len;
    return;
  }

  if (ctx->data_used != 0) {
    const size_t todo = sizeof(ctx->data) - ctx->data_used;
    OPENSSL_memcpy(&ctx->data[ctx->data_used], in, todo);
    in += todo;
    in_len -= todo;

    size_t encoded = EVP_EncodeBlock(out, ctx->data, sizeof(ctx->data));
    ctx->data_used = 0;

    out += encoded;
    *(out++) = '\n';
    *out = '\0';

    total = encoded + 1;
  }

  while (in_len >= sizeof(ctx->data)) {
    size_t encoded = EVP_EncodeBlock(out, in, sizeof(ctx->data));
    in += sizeof(ctx->data);
    in_len -= sizeof(ctx->data);

    out += encoded;
    *(out++) = '\n';
    *out = '\0';

    if (total + encoded + 1 < total) {
      *out_len = 0;
      return;
    }

    total += encoded + 1;
  }

  if (in_len != 0) {
    OPENSSL_memcpy(ctx->data, in, in_len);
  }

  ctx->data_used = (unsigned)in_len;

  if (total > INT_MAX) {
    // We cannot signal an error, but we can at least avoid making *out_len
    // negative.
    total = 0;
  }
  *out_len = (int)total;
}

void EVP_EncodeFinal(EVP_ENCODE_CTX *ctx, uint8_t *out, int *out_len) {
  if (ctx->data_used == 0) {
    *out_len = 0;
    return;
  }

  size_t encoded = EVP_EncodeBlock(out, ctx->data, ctx->data_used);
  out[encoded++] = '\n';
  out[encoded] = '\0';
  ctx->data_used = 0;

  // ctx->data_used is bounded by sizeof(ctx->data), so this does not
  // overflow.
  assert(encoded <= INT_MAX);
  *out_len = (int)encoded;
}

size_t EVP_EncodeBlock(uint8_t *dst, const uint8_t *src, size_t src_len) {
  uint32_t l;
  size_t remaining = src_len, ret = 0;

  while (remaining) {
    if (remaining >= 3) {
      l = (((uint32_t)src[0]) << 16L) | (((uint32_t)src[1]) << 8L) | src[2];
      *(dst++) = conv_bin2ascii(l >> 18L);
      *(dst++) = conv_bin2ascii(l >> 12L);
      *(dst++) = conv_bin2ascii(l >> 6L);
      *(dst++) = conv_bin2ascii(l);
      remaining -= 3;
    } else {
      l = ((uint32_t)src[0]) << 16L;
      if (remaining == 2) {
        l |= ((uint32_t)src[1] << 8L);
      }

      *(dst++) = conv_bin2ascii(l >> 18L);
      *(dst++) = conv_bin2ascii(l >> 12L);
      *(dst++) = (remaining == 1) ? '=' : conv_bin2ascii(l >> 6L);
      *(dst++) = '=';
      remaining = 0;
    }
    ret += 4;
    src += 3;
  }

  *dst = '\0';
  return ret;
}


// Decoding.

int EVP_DecodedLength(size_t *out_len, size_t len) {
  if (len % 4 != 0) {
    return 0;
  }

  *out_len = (len / 4) * 3;
  return 1;
}

void EVP_DecodeInit(EVP_ENCODE_CTX *ctx) {
  OPENSSL_memset(ctx, 0, sizeof(EVP_ENCODE_CTX));
}

static uint8_t base64_ascii_to_bin(uint8_t a) {
  // Since PEM is sometimes used to carry private keys, we decode base64 data
  // itself in constant-time.
  const uint8_t is_upper = constant_time_in_range_8(a, 'A', 'Z');
  const uint8_t is_lower = constant_time_in_range_8(a, 'a', 'z');
  const uint8_t is_digit = constant_time_in_range_8(a, '0', '9');
  const uint8_t is_plus = constant_time_eq_8(a, '+');
  const uint8_t is_slash = constant_time_eq_8(a, '/');
  const uint8_t is_equals = constant_time_eq_8(a, '=');

  uint8_t ret = 0;
  ret |= is_upper & (a - 'A');       // [0,26)
  ret |= is_lower & (a - 'a' + 26);  // [26,52)
  ret |= is_digit & (a - '0' + 52);  // [52,62)
  ret |= is_plus & 62;
  ret |= is_slash & 63;
  // Invalid inputs, 'A', and '=' have all been mapped to zero. Map invalid
  // inputs to 0xff. Note '=' is padding and handled separately by the caller.
  const uint8_t is_valid =
      is_upper | is_lower | is_digit | is_plus | is_slash | is_equals;
  ret |= ~is_valid;
  return ret;
}

// base64_decode_quad decodes a single “quad” (i.e. four characters) of base64
// data and writes up to three bytes to |out|. It sets |*out_num_bytes| to the
// number of bytes written, which will be less than three if the quad ended
// with padding.  It returns one on success or zero on error.
static int base64_decode_quad(uint8_t *out, size_t *out_num_bytes,
                              const uint8_t *in) {
  const uint8_t a = base64_ascii_to_bin(in[0]);
  const uint8_t b = base64_ascii_to_bin(in[1]);
  const uint8_t c = base64_ascii_to_bin(in[2]);
  const uint8_t d = base64_ascii_to_bin(in[3]);
  if (a == 0xff || b == 0xff || c == 0xff || d == 0xff) {
    return 0;
  }

  const uint32_t v = ((uint32_t)a) << 18 | ((uint32_t)b) << 12 |
                     ((uint32_t)c) << 6 | (uint32_t)d;

  const unsigned padding_pattern = (in[0] == '=') << 3 | //
                                   (in[1] == '=') << 2 | //
                                   (in[2] == '=') << 1 | //
                                   (in[3] == '=');

  // In presence of padding, the lowest bits of v are unused. Canonical encoding
  // (RFC 4648, section 3.5) requires that these bits all be set to zero. Common
  // PEM parsers accept noncanonical base64, adding to the malleability of the
  // format. This decoder follows OpenSSL's and Go's PEM parsers and accepts it.
  switch (padding_pattern) {
    case 0:
      // The common case of no padding.
      *out_num_bytes = 3;
      out[0] = v >> 16;
      out[1] = v >> 8;
      out[2] = v;
      break;

    case 1:  // xxx=
      *out_num_bytes = 2;
      out[0] = v >> 16;
      out[1] = v >> 8;
      break;

    case 3:  // xx==
      *out_num_bytes = 1;
      out[0] = v >> 16;
      break;

    default:
      return 0;
  }

  return 1;
}

int EVP_DecodeUpdate(EVP_ENCODE_CTX *ctx, uint8_t *out, int *out_len,
                     const uint8_t *in, size_t in_len) {
  *out_len = 0;

  if (ctx->error_encountered) {
    return -1;
  }

  size_t bytes_out = 0, i;
  for (i = 0; i < in_len; i++) {
    const char c = in[i];
    switch (c) {
      case ' ':
      case '\t':
      case '\r':
      case '\n':
        continue;
    }

    if (ctx->eof_seen) {
      ctx->error_encountered = 1;
      return -1;
    }

    ctx->data[ctx->data_used++] = c;
    if (ctx->data_used == 4) {
      size_t num_bytes_resulting;
      if (!base64_decode_quad(out, &num_bytes_resulting, ctx->data)) {
        ctx->error_encountered = 1;
        return -1;
      }

      ctx->data_used = 0;
      bytes_out += num_bytes_resulting;
      out += num_bytes_resulting;

      if (num_bytes_resulting < 3) {
        ctx->eof_seen = 1;
      }
    }
  }

  if (bytes_out > INT_MAX) {
    ctx->error_encountered = 1;
    *out_len = 0;
    return -1;
  }
  *out_len = (int)bytes_out;

  if (ctx->eof_seen) {
    return 0;
  }

  return 1;
}

int EVP_DecodeFinal(EVP_ENCODE_CTX *ctx, uint8_t *out, int *out_len) {
  *out_len = 0;
  if (ctx->error_encountered || ctx->data_used != 0) {
    return -1;
  }

  return 1;
}

int EVP_DecodeBase64(uint8_t *out, size_t *out_len, size_t max_out,
                     const uint8_t *in, size_t in_len) {
  *out_len = 0;

  if (in_len % 4 != 0) {
    return 0;
  }

  size_t max_len;
  if (!EVP_DecodedLength(&max_len, in_len) || max_out < max_len) {
    return 0;
  }

  size_t i, bytes_out = 0;
  for (i = 0; i < in_len; i += 4) {
    size_t num_bytes_resulting;

    if (!base64_decode_quad(out, &num_bytes_resulting, &in[i])) {
      return 0;
    }

    bytes_out += num_bytes_resulting;
    out += num_bytes_resulting;
    if (num_bytes_resulting != 3 && i != in_len - 4) {
      return 0;
    }
  }

  *out_len = bytes_out;
  return 1;
}

int EVP_DecodeBlock(uint8_t *dst, const uint8_t *src, size_t src_len) {
  // Trim spaces and tabs from the beginning of the input.
  while (src_len > 0) {
    if (src[0] != ' ' && src[0] != '\t') {
      break;
    }

    src++;
    src_len--;
  }

  // Trim newlines, spaces and tabs from the end of the line.
  while (src_len > 0) {
    switch (src[src_len - 1]) {
      case ' ':
      case '\t':
      case '\r':
      case '\n':
        src_len--;
        continue;
    }

    break;
  }

  size_t dst_len;
  if (!EVP_DecodedLength(&dst_len, src_len) || dst_len > INT_MAX ||
      !EVP_DecodeBase64(dst, &dst_len, dst_len, src, src_len)) {
    return -1;
  }

  // EVP_DecodeBlock does not take padding into account, so put the
  // NULs back in... so the caller can strip them back out.
  while (dst_len % 3 != 0) {
    dst[dst_len++] = '\0';
  }
  assert(dst_len <= INT_MAX);

  return (int)dst_len;
}