公司需要自己課件疮丛，講義等文件只能由自己的app打開幔嫂，不能夠由別的工具打開辆它，防止盜版。主要是pdf
無論是音頻履恩，視頻锰茉，文本文件，本質(zhì)只不過是一堆二進(jìn)制數(shù)據(jù)切心，之所以能夠被播放和閱讀洞辣，是因?yàn)檫@些二進(jìn)制數(shù)據(jù)都按照有自己特定的格式組合了數(shù)據(jù)，相應(yīng)的軟件可以根據(jù)約定好的格式去解析里面的數(shù)據(jù)然后呈現(xiàn)出相應(yīng)的結(jié)果昙衅。
pdf結(jié)構(gòu)格式介紹參考:
http://blog.csdn.net/pdfmaker/article/details/573990
同時(shí)可以使用工具PDFStreamDumper查看對(duì)應(yīng)的結(jié)構(gòu)扬霜。根據(jù)里面的結(jié)構(gòu)依次讀取二進(jìn)制文件信息結(jié)合pdf協(xié)議就可以制作pdf閱讀器，但是這應(yīng)該不是一個(gè)簡(jiǎn)單的事情而涉。pdf文件是支持設(shè)定密碼的著瓶，但是這里的需求不是用pdf自帶的密碼機(jī)制，而是希望對(duì)文件進(jìn)行加密啼县〔脑可以參考http://blog.csdn.net/pdfMaker/article/details/576210 在pdf格式的基礎(chǔ)上增加字段自定義自己的格式，但是有點(diǎn)復(fù)雜季眷，而且文中所介紹的pdf加密主要是對(duì)于普通用戶設(shè)置密碼和這里需求也不太一樣余蟹，如果這樣需要實(shí)現(xiàn)用戶口令驗(yàn)證算法和pdf加密算法。這兩個(gè)算法需要自己設(shè)計(jì)子刮，而且不能太簡(jiǎn)單威酒，因?yàn)閜df文件格式不像視頻那樣復(fù)雜惰蜜，所有的密碼信息都再文本中史侣，過于簡(jiǎn)單容易破解。而且課件還可能是ppt暇榴，如果用這樣的辦法加密ppt文件是不可行的橱赠。所有考慮到應(yīng)該對(duì)整個(gè)文件進(jìn)行加密尤仍。使用AES加密算法，下面的是AES算法是aes/ecb/pck5padding+base64
php 端
案例
header("Content-type: text/html; charset=utf-8");
require_once 'aes.php';
$content = file_get_contents('group.pdf');
$aes = new Security('1234567812345678', '');//密碼長(zhǎng)度16位
$res = $aes->encrypt($content);
file_put_contents('encrypt_pdf.pdf', $res);
php 加密類
class Security {
private $key = null;
private $signKey = null;
/**
*
* @param $key 密鑰
* @return String
*/
public function __construct($key = null, $signKey = null) {
if(is_null($key)) {
throw new \Exception('set sccret key please.');
}
if(is_null($signKey)) {
throw new \Exception('set sign key please.');
}
$this->key = $key;
$this->signKey = $signKey;
}
/**
* 加密
* @param String input 加密的字符串
* @param String key 解密的key
* @return HexString
*/
public function encrypt($input) {
$size = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_ECB);
$input = $this->pkcs5_pad($input, $size);
$td = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_ECB, '');
$iv = mcrypt_create_iv(mcrypt_enc_get_iv_size($td), MCRYPT_RAND);
mcrypt_generic_init($td, $this->key, $iv);
$data = mcrypt_generic($td, $input);
mcrypt_generic_deinit($td);
mcrypt_module_close($td);
$data = base64_encode($data);
return $data;
}
/**
* 填充方式 pkcs5
* @param String text 原始字符串
* @param String blocksize 加密長(zhǎng)度
* @return String
*/
private function pkcs5_pad($text, $blocksize) {
$pad = $blocksize - (strlen($text) % $blocksize);
return $text . str_repeat(chr($pad), $pad);
}
/**
* 解密
* @param String input 解密的字符串
* @param String key 解密的key
* @return String
*/
public function decrypt($sStr) {
$decrypted= mcrypt_decrypt(MCRYPT_RIJNDAEL_128,$this->key,base64_decode($sStr), MCRYPT_MODE_ECB);
$dec_s = strlen($decrypted);
$padding = ord($decrypted[$dec_s-1]);
$decrypted = substr($decrypted, 0, -$padding);
return $decrypted;
}
}
iOS客戶端
使用了Reader 庫(kù):https://github.com/vfr/Reader狭姨，這是一個(gè)非常強(qiáng)大的開源pdf閱讀器宰啦。經(jīng)過研究發(fā)現(xiàn)系統(tǒng)加載pdf文件可以通過二進(jìn)制也可以通過文本路徑，所有我們可以以二進(jìn)制的方式讀取文件饼拍，先得到二進(jìn)制數(shù)據(jù)赡模，然后對(duì)NSData進(jìn)行解密后交給Reader庫(kù)處理。通過觀察可以發(fā)現(xiàn)該庫(kù)判斷一個(gè)文件是不是pdf就是根據(jù)pdf文件格式的前面部分是否包含pdf版本信息來確定的惕耕，加密后的文件是不會(huì)包含這些信息的纺裁，所以這可以作為是否加密的依據(jù)，這樣就可以同時(shí)打開加密的和不加密文件了。
更改 ReadContentPage.m 文件
- (instancetype)initWithURL:(NSURL *)fileURL page:(NSInteger)page password:(NSString *)phrase
_PDFDocRef = CGPDFDocumentCreateUsingUrl((__bridge CFURLRef)fileURL, phrase);
if (!_PDFDocRef) {
NSData * data = [NSData dataWithContentsOfURL:fileURL]; // CFURLRef from NSURL
NSString *base64Encoded = [[NSString alloc]
initWithData:data encoding:NSUTF8StringEncoding];
data = [[NSData alloc]
initWithBase64EncodedString:base64Encoded options:0];
data = [data AES256_Decrypt:@"1234567812345678"];;
_PDFDocRef = CGPDFDocumentCreateUsingData(CGDataProviderCreateWithCFData((CFDataRef)data), phrase);
}
更改 ReaderDocument.m
- (instancetype)initWithFilePath:(NSString *)filePath password:(NSString *)phrase {
if ([ReaderDocument isPDF:filePath] == YES) {
CFURLRef docURLRef = (__bridge CFURLRef)[self fileURL]; // CFURLRef from NSURL
thePDFDocRef = CGPDFDocumentCreateUsingUrl(docURLRef, _password);
} else {
NSData * data = [NSData dataWithContentsOfFile:filePath]; // CFURLRef from NSURL
NSString *base64Encoded = [[NSString alloc]
initWithData:data encoding:NSUTF8StringEncoding];
data = [[NSData alloc]
initWithBase64EncodedString:base64Encoded options:0];
data = [data AES256_Decrypt:@"1234567812345678"];;
thePDFDocRef = CGPDFDocumentCreateUsingData( CGDataProviderCreateWithCFData((CFDataRef)data), _password);
}
}
iOS客戶端加密代碼 ：
@interface NSString (AES)
- (NSString *) AES256_Encrypt:(NSString *)key;
- (NSString *) AES256_Decrypt:(NSString *)key;
- (NSString *)stringFromByte:(Byte)byteVal;
- (NSString *)hexStringFromData:(NSData *)data;
@end
//
// NSString+AES.m
// UIImage+PDF example
//
// Created by Me on 17/7/2.
//
//
#import "NSString+AES.h"
#import "NSData+AES.h"
@implementation NSString (AES)
- (NSString *) AES256_Encrypt:(NSString *)key{
const char *cstr = [self cStringUsingEncoding:NSUTF8StringEncoding];
NSData *data = [NSData dataWithBytes:cstr length:self.length];
//對(duì)數(shù)據(jù)進(jìn)行加密
NSData *result = [data AES256_Encrypt:key];
//轉(zhuǎn)換為2進(jìn)制字符串
if (result && result.length > 0) {
Byte *datas = (Byte*)[result bytes];
NSMutableString *output = [NSMutableString stringWithCapacity:result.length * 2];
for(int i = 0; i < result.length; i++){
[output appendFormat:@"%02x", datas[i]];
}
return output;
}
return nil;
}
//解密
- (NSString *) AES256_Decrypt:(NSString *)key{
//轉(zhuǎn)換為2進(jìn)制Data
NSMutableData *data = [NSMutableData dataWithCapacity:self.length / 2];
unsigned char whole_byte;
char byte_chars[3] = {'\0','\0','\0'};
int i;
for (i=0; i < [self length] / 2; i++) {
byte_chars[0] = [self characterAtIndex:i*2];
byte_chars[1] = [self characterAtIndex:i*2+1];
whole_byte = strtol(byte_chars, NULL, 16);
[data appendBytes:&whole_byte length:1];
}
//對(duì)數(shù)據(jù)進(jìn)行解密
NSData* result = [data AES256_Decrypt:key];
if (result && result.length > 0) {
return [[NSString alloc] initWithData:result encoding:NSUTF8StringEncoding];
}
return nil;
}
- (NSString *)stringFromByte:(Byte)byteVal
{
NSMutableString *str = [NSMutableString string];
//取高四位
Byte byte1 = byteVal>>4;
//取低四位
Byte byte2 = byteVal & 0xf;
//拼接16進(jìn)制字符串
[str appendFormat:@"%x",byte1];
[str appendFormat:@"%x",byte2];
return str;
}
- (NSString *)hexStringFromData:(NSData *)data
{
NSMutableString *str = [NSMutableString string];
Byte *byte = (Byte *)[data bytes];
for (int i = 0; i<[data length]; i++) {
// byte+i為指針
[str appendString:[self stringFromByte:*(byte+i)]];
}
return str;
}
@end
//
// NSData+AES.h
// UIImage+PDF example
//
// Created by Me on 17/7/2.
//
//
#import <Foundation/Foundation.h>
#import <CommonCrypto/CommonDigest.h>
#import <CommonCrypto/CommonCryptor.h>
@interface NSData (AES)
- (NSData *) AES256_Encrypt:(NSString *)key;
- (NSData *) AES256_Decrypt:(NSString *)key;
- (NSString *)newStringInBase64FromData;
+(NSString*)base64encode:(NSString*)str;
- (NSData *)dataFromHexString:(NSString *)hexStr;
@end
//
// NSData+AES.m
// UIImage+PDF example
//
// Created by 王國(guó)棟 on 17/7/2.
//
//
#import "NSData+AES.h"
static char base64[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
@implementation NSData (AES)
- (NSData *) AES256_Encrypt:(NSString *)key{
char keyPtr[kCCKeySizeAES256+1];
bzero(keyPtr, sizeof(keyPtr));
[key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
NSUInteger dataLength = [self length];
size_t bufferSize = dataLength + kCCBlockSizeAES128;
void *buffer = malloc(bufferSize);
size_t numBytesEncrypted = 0;
CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128,
kCCOptionPKCS7Padding | kCCOptionECBMode,
keyPtr, kCCBlockSizeAES128,
NULL,
[self bytes], dataLength,
buffer, bufferSize,
&numBytesEncrypted);
if (cryptStatus == kCCSuccess) {
return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
}
free(buffer);
return nil;
}
- (NSData *) AES256_Decrypt:(NSString *)key{
char keyPtr[kCCKeySizeAES256+1];
bzero(keyPtr, sizeof(keyPtr));
[key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
NSUInteger dataLength = [self length];
size_t bufferSize = dataLength + kCCBlockSizeAES128;
void *buffer = malloc(bufferSize);
size_t numBytesDecrypted = 0;
CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt, kCCAlgorithmAES128,
kCCOptionPKCS7Padding | kCCOptionECBMode,
keyPtr, kCCBlockSizeAES128,
NULL,
[self bytes], dataLength,
buffer, bufferSize,
&numBytesDecrypted);
if (cryptStatus == kCCSuccess) {
return [NSData dataWithBytesNoCopy:buffer length:numBytesDecrypted];
}
free(buffer);
return nil;
}
- (NSString *)newStringInBase64FromData
{
NSMutableString *dest = [[NSMutableString alloc] initWithString:@""];
unsigned char * working = (unsigned char *)[self bytes];
int srcLen = (int)[self length];
for (int i=0; i<srcLen; i += 3) {
for (int nib=0; nib<4; nib++) {
int byt = (nib == 0)?0:nib-1;
int ix = (nib+1)*2;
if (i+byt >= srcLen)
break;
unsigned char curr = ((working[i+byt] << (8-ix)) & 0x3F);
if (i+nib < srcLen) curr |= ((working[i+nib] >> ix) & 0x3F);
[dest appendFormat:@"%c", base64[curr]];
}
}
return dest;
}
+ (NSString*)base64encode:(NSString*)str
{
if ([str length] == 0)
return @"";
const char *source = [str UTF8String];
int strlength = (int)strlen(source);
char *characters = malloc(((strlength + 2) / 3) * 4);
if (characters == NULL)
return nil;
NSUInteger length = 0;
NSUInteger i = 0;
while (i < strlength) {
char buffer[3] = {0,0,0};
short bufferLength = 0;
while (bufferLength < 3 && i < strlength)
buffer[bufferLength++] = source[i++];
characters[length++] = base64[(buffer[0] & 0xFC) >> 2];
characters[length++] = base64[((buffer[0] & 0x03) << 4) | ((buffer[1] & 0xF0) >> 4)];
if (bufferLength > 1)
characters[length++] = base64[((buffer[1] & 0x0F) << 2) | ((buffer[2] & 0xC0) >> 6)];
else characters[length++] = '=';
if (bufferLength > 2)
characters[length++] = base64[buffer[2] & 0x3F];
else characters[length++] = '=';
}
NSString *g = [[NSString alloc] initWithBytesNoCopy:characters length:length encoding:NSASCIIStringEncoding freeWhenDone:YES];
return g;
}
@end
算法升級(jí)
上面的是固定密鑰欺缘，不安全栋豫。可以考慮每個(gè)文件一個(gè)密鑰谚殊，可以由服務(wù)器記錄每個(gè)文件和對(duì)應(yīng)的密鑰丧鸯，但是麻煩。所以可以考慮到把密鑰進(jìn)行加密后寫在文件的末尾或者頭部嫩絮，客戶端直接從相應(yīng)位置提取丛肢，根據(jù)相應(yīng)的算法先解密密鑰，比如可以使用RSA算法加密密鑰剿干。服務(wù)器用公鑰加密蜂怎，客戶端保存私鑰。
