utilities/src/der_number.c

   1 //
   2 //  der_number.c
   3 //  utilities
   4 //
   5 //  Created by Mitch Adler on 6/19/12.
   6 //  Copyright (c) 2012 Apple Inc. All rights reserved.
   7 //
   8
   9
  10 #include <stdio.h>
  11
  12 #include "utilities/SecCFRelease.h"
  13 #include "utilities/der_plist.h"
  14 #include "utilities/der_plist_internal.h"
  15
  16 #include <corecrypto/ccder.h>
  17 #include <CoreFoundation/CoreFoundation.h>
  18
  19
  20 const uint8_t* der_decode_number(CFAllocatorRef allocator, CFOptionFlags mutability,
  21                                  CFNumberRef* number, CFErrorRef *error,
  22                                  const uint8_t* der, const uint8_t *der_end)
  23 {
  24     if (NULL == der)
  25         return NULL;
  26
  27     size_t payload_size = 0;
  28     const uint8_t *payload = ccder_decode_tl(CCDER_INTEGER, &payload_size, der, der_end);
  29
  30     if (NULL == payload || (der_end - payload) < payload_size) {
  31         SecCFDERCreateError(kSecDERErrorUnknownEncoding, CFSTR("Unknown number encoding"), NULL, error);
  32         return NULL;
  33     }
  34     if (payload_size > sizeof(long long)) {
  35         SecCFDERCreateError(kSecDERErrorUnsupportedNumberType, CFSTR("Number too large"), NULL, error);
  36         return NULL;
  37
  38     }
  39
  40     long long value = 0;
  41
  42     if (payload_size > 0) {
  43         if ((*payload & 0x80) == 0x80)
  44             value = -1; // Negative integers fill with 1s so we end up negative.
  45
  46         const uint8_t* const payload_end = payload + payload_size;
  47
  48         for (const uint8_t *payload_byte = payload;
  49              payload_byte < payload_end;
  50              ++payload_byte) {
  51             value <<= 8;
  52             value |= *payload_byte;
  53         }
  54     }
  55
  56     *number = CFNumberCreate(allocator, kCFNumberLongLongType, &value);
  57
  58     if (*number == NULL) {
  59         SecCFDERCreateError(kSecDERErrorAllocationFailure, CFSTR("Number allocation failed"), NULL, error);
  60         return NULL;
  61     }
  62
  63     return payload + payload_size;
  64 }
  65
  66
  67 static inline uint8_t byte_of(size_t byteNumber, long long value)
  68 {
  69     return value >> (8 * (byteNumber - 1));
  70 }
  71
  72 static inline size_t bytes_when_encoded(long long value)
  73 {
  74     size_t bytes_encoded = sizeof(long long);
  75
  76     uint8_t first_byte = byte_of(bytes_encoded, value);
  77
  78     // Skip initial 0xFFs or 0x00
  79     if (first_byte == 0xFF || first_byte == 0x00) {
  80         do {
  81             --bytes_encoded;
  82         } while (bytes_encoded > 1 && (byte_of(bytes_encoded, value) == first_byte));
  83
  84         if ((first_byte & 0x80) != (byte_of(bytes_encoded, value) & 0x80))
  85             bytes_encoded += 1;
  86     }
  87
  88     return bytes_encoded;
  89 }
  90
  91 size_t der_sizeof_number(CFNumberRef data, CFErrorRef *error)
  92 {
  93     long long value;
  94     if (!CFNumberGetValue(data, kCFNumberLongLongType, &value))
  95         return 0;
  96
  97     return ccder_sizeof(CCDER_INTEGER, bytes_when_encoded(value));
  98 }
  99
 100 uint8_t* der_encode_number(CFNumberRef number, CFErrorRef *error,
 101                            const uint8_t *der, uint8_t *der_end)
 102 {
 103     long long value;
 104     if (!CFNumberGetValue(number, kCFNumberLongLongType, &value))
 105         return NULL;
 106
 107     size_t first_byte_to_include = bytes_when_encoded(value);
 108
 109     if (!der_end || der_end - der < first_byte_to_include)
 110         return NULL;
 111
 112     // Put the bytes we should include on the end.
 113     for(int bytes_included = 0; bytes_included < first_byte_to_include; ++bytes_included)
 114     {
 115         --der_end;
 116         *der_end = value & 0xFF;
 117         value >>= 8;
 118     }
 119
 120     return ccder_encode_tl(CCDER_INTEGER, first_byte_to_include, der, der_end);
 121
 122 }