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
20const 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
67static inline uint8_t byte_of(size_t byteNumber, long long value)
68{
69    return value >> (8 * (byteNumber - 1));
70}
71
72static 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
91size_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
100uint8_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}
123