iOS RSA加密算法详解：保障iOS应用数据传输安全

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<e< φ(n)，且e与φ(n)互质。

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。