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19 * Portions Copyright (c) 1995 by International Business Machines, Inc.
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42 #include <ldns/config.h>
47 static const char Base64[] =
48 "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
49 static const char Pad64 = '=';
51 /* (From RFC1521 and draft-ietf-dnssec-secext-03.txt)
52 The following encoding technique is taken from RFC 1521 by Borenstein
53 and Freed. It is reproduced here in a slightly edited form for
56 A 65-character subset of US-ASCII is used, enabling 6 bits to be
57 represented per printable character. (The extra 65th character, "=",
58 is used to signify a special processing function.)
60 The encoding process represents 24-bit groups of input bits as output
61 strings of 4 encoded characters. Proceeding from left to right, a
62 24-bit input group is formed by concatenating 3 8-bit input groups.
63 These 24 bits are then treated as 4 concatenated 6-bit groups, each
64 of which is translated into a single digit in the base64 alphabet.
66 Each 6-bit group is used as an index into an array of 64 printable
67 characters. The character referenced by the index is placed in the
70 Table 1: The Base64 Alphabet
72 Value Encoding Value Encoding Value Encoding Value Encoding
87 14 O 31 f 48 w (pad) =
91 Special processing is performed if fewer than 24 bits are available
92 at the end of the data being encoded. A full encoding quantum is
93 always completed at the end of a quantity. When fewer than 24 input
94 bits are available in an input group, zero bits are added (on the
95 right) to form an integral number of 6-bit groups. Padding at the
96 end of the data is performed using the '=' character.
98 Since all base64 input is an integral number of octets, only the
99 -------------------------------------------------
100 following cases can arise:
102 (1) the final quantum of encoding input is an integral
103 multiple of 24 bits; here, the final unit of encoded
104 output will be an integral multiple of 4 characters
106 (2) the final quantum of encoding input is exactly 8 bits;
107 here, the final unit of encoded output will be two
108 characters followed by two "=" padding characters, or
109 (3) the final quantum of encoding input is exactly 16 bits;
110 here, the final unit of encoded output will be three
111 characters followed by one "=" padding character.
115 ldns_b64_ntop(uint8_t const *src, size_t srclength, char *target, size_t targsize) {
116 size_t datalength = 0;
121 if (srclength == 0) {
130 while (2 < srclength) {
136 output[0] = input[0] >> 2;
137 output[1] = ((input[0] & 0x03) << 4) + (input[1] >> 4);
138 output[2] = ((input[1] & 0x0f) << 2) + (input[2] >> 6);
139 output[3] = input[2] & 0x3f;
140 assert(output[0] < 64);
141 assert(output[1] < 64);
142 assert(output[2] < 64);
143 assert(output[3] < 64);
145 if (datalength + 4 > targsize) {
148 target[datalength++] = Base64[output[0]];
149 target[datalength++] = Base64[output[1]];
150 target[datalength++] = Base64[output[2]];
151 target[datalength++] = Base64[output[3]];
154 /* Now we worry about padding. */
155 if (0 != srclength) {
156 /* Get what's left. */
157 input[0] = input[1] = input[2] = (uint8_t) '\0';
158 for (i = 0; i < srclength; i++)
161 output[0] = input[0] >> 2;
162 output[1] = ((input[0] & 0x03) << 4) + (input[1] >> 4);
163 output[2] = ((input[1] & 0x0f) << 2) + (input[2] >> 6);
164 assert(output[0] < 64);
165 assert(output[1] < 64);
166 assert(output[2] < 64);
168 if (datalength + 4 > targsize) {
171 target[datalength++] = Base64[output[0]];
172 target[datalength++] = Base64[output[1]];
173 if (srclength == 1) {
174 target[datalength++] = Pad64;
176 target[datalength++] = Base64[output[2]];
178 target[datalength++] = Pad64;
180 if (datalength >= targsize) {
183 target[datalength] = '\0'; /* Returned value doesn't count \0. */
184 return (int) (datalength);