C语言版的Base-64加密解密函数

概述C语言版的Base-64加密解密函数

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#include <stdint.h>#include <stdlib.h>#include <string.h>#define BLOCK_BYTE       3  // Number of bytes in each base-64 24-bit block#define BLOCK_CHAR       4  // Number of base-64 characters in a 24-bit block#define BASE64_liNE_LEN  76 // Maximum line length of a base-64 string#define NEWliNE_LEN      2  // Number of characters in the newline sequencestatic const char *digits = "ABCDEFGHIJKLMnopQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";static const char *newline = "\r\n";static const char padding = '=';static size_t digit_value(char ch);static voID check_append_newline(char *dst,size_t *end);static voID convert_block(char *dst,size_t *end,const uint8_t *src,size_t bytes);/*    @description:        Converts n bytes pointed to by src into base-64 representation.*/extern char *encode_base64(const voID *src,size_t n){    size_t partial_block_bytes = n % BLOCK_BYTE;    size_t full_blocks = n / BLOCK_BYTE;    // Make room for all full blocks plus one extra for a partial block    char *dst = malloc((full_blocks + 1) * BLOCK_CHAR + 1);    if (!dst)        return NulL;    const uint8_t *bytes = src;    size_t k;    // Convert all complete 24-bit blocks to base-64    for (k = 0; full_blocks--; bytes += BLOCK_BYTE) {        check_append_newline(dst + k,&k);        convert_block(dst,&k,bytes,BLOCK_BYTE);    }    // Convert the final (possibly empty) partial block    check_append_newline(dst + k,&k);    convert_block(dst,partial_block_bytes);    dst[k] = '';    return dst;}/*    @description:        Converts a valID base-64 string into a decoded array of bytes        and stores the number of decoded bytes in the object pointed        to by n.*/extern voID *decode_base64(const char *src,size_t *n){    size_t len = strlen(src);    if (len % BLOCK_CHAR)        return NulL; // InvalID number of base-64 characters    // There will never be more bytes than base-64 characters by deFinition    uint8_t *dst = malloc(len + 1);    for (*n = 0; *src; src += BLOCK_CHAR) {        if (*src == '\r') {            ++src; // Skip the CR part of CRLF            if (*src != '\n') {                free(dst);                return NulL; // Unmatched CR            }            ++src; // Skip the LF part of CRLF        }        size_t encoded[] = {            digit_value(src[0]),digit_value(src[1]),digit_value(src[2]),digit_value(src[3])        };        // Check for invalID base-64 characters        for (size_t i = 0; i < sizeof encoded / sizeof *encoded; ++i) {            if (encoded[i] == (size_t)-1) {                free(dst);                return NulL;            }        }        // Precompute the decoded bytes to faciliate handling of zero byte values        uint8_t bytes[] = {            (encoded[0] << 2) + ((encoded[1] & 0x30) >> 4),((encoded[1] & 0x0f) << 4) + ((encoded[2] & 0x3c) >> 2),((encoded[2] & 0x03) << 6) + encoded[3]        };        // Push non-zero decoded bytes into the destination        for (size_t i = 0; i < BLOCK_BYTE; ++i) {            // Zero bytes should only occur for padding,which we don't save            if (bytes[i])                dst[(*n)++] = bytes[i];        }    }    return dst;}/*    @description:        Locates the index value of a base-64 character for deCoding.*/static size_t digit_value(char ch){    if (ch == padding)        return 0;    const char *p = strchr(digits,ch);    return p ? p - digits : (size_t)-1;}/*    @description:        Appends a newline to dst if the value of end is at the correct        position. Returns the updated value of end,which may not change        if a newline was not appended.*/static voID check_append_newline(char *dst,size_t *end){    if ((*end + 1) % BASE64_liNE_LEN == 0) {        memcpy(dst,newline,NEWliNE_LEN);        *end += NEWliNE_LEN;    }}/*    @description:        Converts a 24-bit block represented by 3 octets into four base-64        characters and stores them in dst starting at end. Returns the        updated value of end for convenIEnce.*/static voID convert_block(char *dst,size_t bytes){    switch (bytes) {        case 3:            dst[(*end)++] = digits[src[0] >> 2];            dst[(*end)++] = digits[((src[0] & 0x03) << 4) | (src[1] >> 4)];            dst[(*end)++] = digits[((src[1] & 0x0f) << 2) | (src[2] >> 6)];            dst[(*end)++] = digits[src[2] & 0x3f];            break;        case 2:            dst[(*end)++] = digits[src[0] >> 2];            dst[(*end)++] = digits[((src[0] & 0x03) << 4) | (src[1] >> 4)];            dst[(*end)++] = digits[((src[1] & 0x0f) << 2)];            dst[(*end)++] = padding;            break;        case 1:            dst[(*end)++] = digits[src[0] >> 2];            dst[(*end)++] = digits[((src[0] & 0x03) << 4)];            dst[(*end)++] = padding;            dst[(*end)++] = padding;            break;    }}#define TEST_DRIVER#ifdef TEST_DRIVER#include <stdbool.h>#include <stdio.h>#include <stdlib.h>#include <string.h>int main(voID){    const char *test[] = {"","f","fo","foo","foob","fooba","foobar"};    size_t n;    for (size_t i = 0; i < sizeof test / sizeof *test; ++i) {        char *p = encode_base64(test[i],strlen(test[i]));        char *q = decode_base64(p,&n);        printf("BASE64(\"%s\") = \"%s\" = (%zd)\"%.*s\"\n",test[i],p,n,q);        free(p);        free(q);    }    return 0;}#endif

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