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s2n_stuffer_base64.c
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s2n_stuffer_base64.c
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/*
* Copyright Amazon.com, Inc. or its affiliates. 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.
* A copy of the License is located at
*
* http://aws.amazon.com/apache2.0
*
* or in the "license" file accompanying this file. This file 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 <string.h>
#include "error/s2n_errno.h"
#include "stuffer/s2n_stuffer.h"
#include "utils/s2n_safety.h"
static const uint8_t b64[64] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q',
'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+',
'/' };
/* Generated with this python:
*
* b64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
*
* for i in range(0, 256):
* if chr(i) in b64:
* print str(b64.index(chr(i))) + ", ",
* else:
* print "255, ",
*
* if (i + 1) % 16 == 0:
* print
*
* Note that '=' maps to 64.
*/
static const uint8_t b64_inverse[256] = { 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 62, 255, 255, 255, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 255, 255, 255, 64, 255, 255,
255, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 255, 255, 255,
255, 255, 255, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50,
51, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255 };
bool s2n_is_base64_char(unsigned char c)
{
return (b64_inverse[*((uint8_t *) (&c))] != 255);
}
/**
* NOTE:
* In general, shift before masking. This avoids needing to worry about how the
* signed bit may be handled.
*/
int s2n_stuffer_read_base64(struct s2n_stuffer *stuffer, struct s2n_stuffer *out)
{
POSIX_PRECONDITION(s2n_stuffer_validate(stuffer));
POSIX_PRECONDITION(s2n_stuffer_validate(out));
int bytes_this_round = 3;
s2n_stack_blob(o, 4, 4);
do {
if (s2n_stuffer_data_available(stuffer) < o.size) {
break;
}
POSIX_GUARD(s2n_stuffer_read(stuffer, &o));
uint8_t value1 = b64_inverse[o.data[0]];
uint8_t value2 = b64_inverse[o.data[1]];
uint8_t value3 = b64_inverse[o.data[2]];
uint8_t value4 = b64_inverse[o.data[3]];
/* We assume the entire thing is base64 data, thus, terminate cleanly if we encounter a non-base64 character */
if (value1 == 255) {
/* Undo the read */
stuffer->read_cursor -= o.size;
POSIX_BAIL(S2N_ERR_INVALID_BASE64);
}
/* The first two characters can never be '=' and in general
* everything has to be a valid character.
*/
POSIX_ENSURE(!(value1 == 64 || value2 == 64 || value2 == 255 || value3 == 255 || value4 == 255),
S2N_ERR_INVALID_BASE64);
if (o.data[2] == '=') {
/* If there is only one output byte, then the second value
* should have none of its bottom four bits set.
*/
POSIX_ENSURE(!(o.data[3] != '=' || value2 & 0x0f), S2N_ERR_INVALID_BASE64);
bytes_this_round = 1;
value3 = 0;
value4 = 0;
} else if (o.data[3] == '=') {
/* The last two bits of the final value should be unset */
POSIX_ENSURE(!(value3 & 0x03), S2N_ERR_INVALID_BASE64);
bytes_this_round = 2;
value4 = 0;
}
/* Advance by bytes_this_round, and then fill in the data */
POSIX_GUARD(s2n_stuffer_skip_write(out, bytes_this_round));
uint8_t *ptr = out->blob.data + out->write_cursor - bytes_this_round;
/* value1 maps to the first 6 bits of the first data byte */
/* value2's top two bits are the rest */
*ptr = ((value1 << 2) & 0xfc) | ((value2 >> 4) & 0x03);
if (bytes_this_round > 1) {
/* Put the next four bits in the second data byte */
/* Put the next four bits in the third data byte */
ptr++;
*ptr = ((value2 << 4) & 0xf0) | ((value3 >> 2) & 0x0f);
}
if (bytes_this_round > 2) {
/* Put the next two bits in the third data byte */
/* Put the next six bits in the fourth data byte */
ptr++;
*ptr = ((value3 << 6) & 0xc0) | (value4 & 0x3f);
}
} while (bytes_this_round == 3);
return S2N_SUCCESS;
}
int s2n_stuffer_write_base64(struct s2n_stuffer *stuffer, struct s2n_stuffer *in)
{
POSIX_PRECONDITION(s2n_stuffer_validate(stuffer));
POSIX_PRECONDITION(s2n_stuffer_validate(in));
s2n_stack_blob(o, 4, 4);
s2n_stack_blob(i, 3, 3);
while (s2n_stuffer_data_available(in) > 2) {
POSIX_GUARD(s2n_stuffer_read(in, &i));
/* Take the top 6-bits of the first data byte */
o.data[0] = b64[(i.data[0] >> 2) & 0x3f];
/* Take the bottom 2-bits of the first data byte - 0b00110000 = 0x30
* and take the top 4-bits of the second data byte - 0b00001111 = 0x0f
*/
o.data[1] = b64[((i.data[0] << 4) & 0x30) | ((i.data[1] >> 4) & 0x0f)];
/* Take the bottom 4-bits of the second data byte - 0b00111100 = 0x3c
* and take the top 2-bits of the third data byte - 0b00000011 = 0x03
*/
o.data[2] = b64[((i.data[1] << 2) & 0x3c) | ((i.data[2] >> 6) & 0x03)];
/* Take the bottom 6-bits of the second data byte - 0b00111111 = 0x3f
*/
o.data[3] = b64[i.data[2] & 0x3f];
POSIX_GUARD(s2n_stuffer_write(stuffer, &o));
}
if (s2n_stuffer_data_available(in)) {
/* Read just one byte */
i.size = 1;
POSIX_GUARD(s2n_stuffer_read(in, &i));
uint8_t c = i.data[0];
/* We at least one data byte left to encode, encode
* its first six bits
*/
o.data[0] = b64[(c >> 2) & 0x3f];
/* And our end has to be an equals */
o.data[3] = '=';
/* How many bytes are actually left? */
if (s2n_stuffer_data_available(in) == 0) {
/* We just have the last two bits to deal with */
o.data[1] = b64[(c << 4) & 0x30];
o.data[2] = '=';
} else {
/* Read the last byte */
POSIX_GUARD(s2n_stuffer_read(in, &i));
o.data[1] = b64[((c << 4) & 0x30) | ((i.data[0] >> 4) & 0x0f)];
o.data[2] = b64[((i.data[0] << 2) & 0x3c)];
}
POSIX_GUARD(s2n_stuffer_write(stuffer, &o));
}
return S2N_SUCCESS;
}