一、什么是RSA算法
RSA算法是一种公钥加密算法，由三个名字的发明者Rivest、Shamir和Adleman共同发明，RSA算法是现代公钥加密算法中最常用的一种，它是一种非对称加密算法，用于数据加密和数字签名。
非对称加密算法需要一对密钥，分别称为公钥和私钥。公钥可以自由发布，私钥则需要保密。任何使用公钥加密的数据，只有使用与之配对的私钥才能解密。RSA算法的主要作用是进行加密和数字签名。
二、RSA算法的加密和解密过程
下面通过以下步骤来介绍RSA算法的加密和解密过程：
1、随机生成两个大素数p和q（通常是1024位或2048位）。
2、计算n=pq，φ(n)=(p-1)(q-1)。
3、随机选取一个整数e，1
4、计算d，使得d×e ≡ 1(mod φ(n))，d为e的逆元。
5、公钥为(n, e)，私钥为(n, d)。
6、加密过程：将明文M转化为整数m，采用公钥(n, e)对明文进行加密，c ≡ m^e (mod n)。
7、解密过程：采用私钥(n, d)对密文进行解密，m ≡ c^d (mod n)。
三、iOS RSA加密算法的实现
在iOS中，可以使用Security.framework提供的API函数实现RSA加密和解密。
四、iOS RSA加密算法示例代码
#include <Security/Security.h>
// RSA加密
+ (NSString *)rsaEncryptString:(NSString *)str publicKey:(NSString *)pubKey {
NSData *plainData = [str dataUsingEncoding:NSUTF8StringEncoding];
SecKeyRef keyRef = [self addPublicKey:pubKey];
size_t cipherBufferSize = SecKeyGetBlockSize(keyRef);
uint8_t *cipherBuffer = malloc(cipherBufferSize);
memset(cipherBuffer, 0, cipherBufferSize);
NSData *pubKeyData = [pubKey dataUsingEncoding:NSUTF8StringEncoding];
NSString *tag = @"RSAEncryption";
NSMutableDictionary *attributes = [[NSMutableDictionary alloc] init];
[attributes setObject:(__bridge id)kSecClassKey forKey:(__bridge id)kSecClass];
[attributes setObject:(__bridge id)kSecAttrKeyTypeRSA forKey:(__bridge id)kSecAttrKeyType];
[attributes setObject:tag forKey:(__bridge id)kSecAttrApplicationTag];
[attributes setObject:pubKeyData forKey:(__bridge id)kSecValueData];
[attributes setObject:@(YES) forKey:(__bridge id)kSecReturnPersistentRef];
CFTypeRef persistKey = nil;
OSStatus status = SecItemAdd((__bridge CFDictionaryRef)attributes, &persistKey);
if (persistKey != nil){
CFRelease(persistKey);
}
if (status != noErr){
return @"";
}
NSData *keyData = [self getPublicKey:pubKey];
SecKeyRef key = [self addPublicKey:keyData];
uint8_t *srcbuf = (uint8_t *)[plainData bytes];
size_t srclen = strlen((char *)srcbuf);
size_t outlen = cipherBufferSize;
OSStatus status1 = SecKeyEncrypt(key, kSecPaddingPKCS1, srcbuf, srclen, &cipherBuffer[0], &outlen);
NSData *cipherData = nil;
if (status1 == noErr){
cipherData = [NSData dataWithBytes:cipherBuffer length:outlen];
}
if (cipherBuffer){
free(cipherBuffer);
}
return [cipherData base64EncodedStringWithOptions:NSDataBase64EncodingEndLineWithLineFeed];
}
// RSA解密
+ (NSString *)rsaDecryptString:(NSString *)str privateKey:(NSString *)privKey {
NSData *cipherData = [[NSData alloc] initWithBase64EncodedString:str options:NSDataBase64DecodingIgnoreUnknownCharacters];
NSData *prikeyData = [privKey dataUsingEncoding:NSUTF8StringEncoding];
SecKeyRef keyRef = [self addPrivateKey:prikeyData];
size_t plainBufferSize = SecKeyGetBlockSize(keyRef);
uint8_t *plainBuffer = malloc(plainBufferSize);
memset(plainBuffer, 0, plainBufferSize);
size_t cipherBufferSize = [cipherData length];
const void *cipherBuffer = [cipherData bytes];
OSStatus status = SecKeyDecrypt(keyRef, kSecPaddingPKCS1, cipherBuffer, cipherBufferSize, plainBuffer, &plainBufferSize);
NSMutableData *decryptedData = nil;
if (status == noErr){
decryptedData = [[NSMutableData alloc] initWithBytes:plainBuffer length:plainBufferSize];
}
if (plainBuffer){
free(plainBuffer);
}
return [[NSString alloc] initWithData:decryptedData encoding:NSUTF8StringEncoding];
}
// 添加公钥
+ (SecKeyRef)addPublicKey:(NSString *)pubKey {
NSRange spos = [pubKey rangeOfString:@"-----BEGIN PUBLIC KEY-----"];
NSRange epos = [pubKey rangeOfString:@"-----END PUBLIC KEY-----"];
if (spos.location != NSNotFound && epos.location != NSNotFound){
NSUInteger s = spos.location + spos.length;
NSUInteger e = epos.location;
NSRange range = NSMakeRange(s, e - s);
pubKey = [pubKey substringWithRange:range];
}
pubKey = [pubKey stringByReplacingOccurrencesOfString:@"\r" withString:@""];
pubKey = [pubKey stringByReplacingOccurrencesOfString:@"\n" withString:@""];
pubKey = [pubKey stringByReplacingOccurrencesOfString:@"\t" withString:@""];
pubKey = [pubKey stringByReplacingOccurrencesOfString:@" " withString:@""];
if (pubKey == nil){
return nil;
}
NSData *data = [[NSData alloc] initWithBase64EncodedString:pubKey options:NSDataBase64DecodingIgnoreUnknownCharacters];
if (data == nil){
return nil;
}
NSMutableDictionary *attributes = [[NSMutableDictionary alloc] init];
[attributes setObject:(__bridge id)kSecClassKey forKey:(__bridge id)kSecClass];
[attributes setObject:(__bridge id)kSecAttrKeyTypeRSA forKey:(__bridge id)kSecAttrKeyType];
[attributes setObject:@(YES) forKey:(__bridge id)kSecReturnPersistentRef];
SecItemDelete((__bridge CFDictionaryRef)attributes);
[attributes setObject:data forKey:(__bridge id)kSecValueData];
SecItemAdd((__bridge CFDictionaryRef)attributes, nil);
[attributes setObject:@(YES) forKey:(__bridge id)kSecReturnRef];
[attributes setObject:(__bridge id)kSecAttrKeyTypeRSA forKey:(__bridge id)kSecAttrKeyType];
SecKeyRef keyRef = nil;
SecItemCopyMatching((__bridge CFDictionaryRef)attributes, (CFTypeRef *)&keyRef);
return keyRef;
}
// 添加私钥
+ (SecKeyRef)addPrivateKey:(NSData *)priKey {
NSMutableDictionary *attributes = [[NSMutableDictionary alloc] init];
[attributes setObject:(__bridge id)kSecClassKey forKey:(__bridge id)kSecClass];
[attributes setObject:(__bridge id)kSecAttrKeyTypeRSA forKey:(__bridge id)kSecAttrKeyType];
[attributes setObject:@(YES) forKey:(__bridge id)kSecReturnPersistentRef];
SecItemDelete((__bridge CFDictionaryRef)attributes);
[attributes setObject:priKey forKey:(__bridge id)kSecValueData];
[attributes setObject:(__bridge id)kSecAttrKeyClassPrivate forKey:(__bridge id)kSecAttrKeyClass];
SecItemAdd((__bridge CFDictionaryRef)attributes, nil);
[attributes removeObjectForKey:(__bridge id)kSecValueData];
[attributes setObject:@(YES) forKey:(__bridge id)kSecReturnRef];
SecKeyRef keyRef = nil;
SecItemCopyMatching((__bridge CFDictionaryRef)attributes, (CFTypeRef *)&keyRef);
return keyRef;
}
// 获取公钥
+ (NSData *)getPublicKey:(NSString *)pubKey {
NSRange spos = [pubKey rangeOfString:@"-----BEGIN PUBLIC KEY-----"];
NSRange epos = [pubKey rangeOfString:@"-----END PUBLIC KEY-----"];
if (spos.location != NSNotFound && epos.location != NSNotFound){
NSUInteger s = spos.location + spos.length;
NSUInteger e = epos.location;
NSRange range = NSMakeRange(s, e - s);
pubKey = [pubKey substringWithRange:range];
}
pubKey = [pubKey stringByReplacingOccurrencesOfString:@"\r" withString:@""];
pubKey = [pubKey stringByReplacingOccurrencesOfString:@"\n" withString:@""];
pubKey = [pubKey stringByReplacingOccurrencesOfString:@"\t" withString:@""];
pubKey = [pubKey stringByReplacingOccurrencesOfString:@" " withString:@""];
if (pubKey == nil){
return nil;
}
NSData *data = [[NSData alloc] initWithBase64EncodedString:pubKey options:NSDataBase64DecodingIgnoreUnknownCharacters];
return data;
}
五、iOS RSA加密算法的应用
iOS RSA加密算法可以应用于iOS应用数据传输安全，例如在iOS应用进行网络请求时，可以将敏感数据通过RSA加密后传输，保障数据传输的安全性。
