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Ios RSA在Objective C中的实现

ios objective-c iphone encryption

Ios RSA在Objective C中的实现,ios,objective-c,iphone,encryption,rsa,Ios,Objective C,Iphone,Encryption,Rsa,我正在objective-C中开发一个使用RSA算法的简单应用程序。我想在服务器/客户端通信中使用它。我需要帮助在iOS/iPhone中实现RSA算法 我有加密和解密的知识 我想要一个开源库或代码添加到我的项目中 我必须通过CommonCryptor.h 我已尝试对NSString进行RSA加密和解密。代码如下： 将Security.Framework添加到项目包中 ViewController.h代码如下： #import <UIKit/UIKit.h> #import <

我正在objective-C中开发一个使用RSA算法的简单应用程序。我想在服务器/客户端通信中使用它。我需要帮助在iOS/iPhone中实现RSA算法

  • 我有加密和解密的知识
  • 我想要一个开源库或代码添加到我的项目中
  • 我必须通过
    CommonCryptor.h
我已尝试对NSString进行RSA加密和解密。代码如下：

将Security.Framework添加到项目包中

ViewController.h代码如下：

#import <UIKit/UIKit.h>
#import <Security/Security.h>

@interface ViewController : UIViewController
{
SecKeyRef publicKey;
SecKeyRef privateKey;
    NSData *publicTag;
    NSData *privateTag;
}
- (void)encryptWithPublicKey:(uint8_t *)plainBuffer cipherBuffer:(uint8_t *)cipherBuffer;
- (void)decryptWithPrivateKey:(uint8_t *)cipherBuffer plainBuffer:(uint8_t *)plainBuffer;
- (SecKeyRef)getPublicKeyRef;
- (SecKeyRef)getPrivateKeyRef;
- (void)testAsymmetricEncryptionAndDecryption;
- (void)generateKeyPair:(NSUInteger)keySize;
@end

#import "ViewController.h"

const size_t BUFFER_SIZE = 64;
const size_t CIPHER_BUFFER_SIZE = 1024;
const uint32_t PADDING = kSecPaddingNone;
static const UInt8 publicKeyIdentifier[] = "com.apple.sample.publickey";
static const UInt8 privateKeyIdentifier[] = "com.apple.sample.privatekey";

@implementation ViewController

-(SecKeyRef)getPublicKeyRef { 

    OSStatus sanityCheck = noErr; 
    SecKeyRef publicKeyReference = NULL;

    if (publicKeyReference == NULL) { 
        [self generateKeyPair:512];
                NSMutableDictionary *queryPublicKey = [[NSMutableDictionary alloc] init];

        // Set the public key query dictionary.
        [queryPublicKey setObject:(__bridge id)kSecClassKey forKey:(__bridge id)kSecClass];
        [queryPublicKey setObject:publicTag forKey:(__bridge id)kSecAttrApplicationTag];
        [queryPublicKey setObject:(__bridge id)kSecAttrKeyTypeRSA forKey:(__bridge id)kSecAttrKeyType];
        [queryPublicKey setObject:[NSNumber numberWithBool:YES] forKey:(__bridge id)kSecReturnRef];


        // Get the key.
        sanityCheck = SecItemCopyMatching((__bridge CFDictionaryRef)queryPublicKey, (CFTypeRef *)&publicKeyReference);


        if (sanityCheck != noErr)
        {
            publicKeyReference = NULL;
        }


//        [queryPublicKey release];

    } else { publicKeyReference = publicKey; }

    return publicKeyReference; }

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Release any cached data, images, etc that aren't in use.
}




- (void)testAsymmetricEncryptionAndDecryption {

    uint8_t *plainBuffer;
    uint8_t *cipherBuffer;
    uint8_t *decryptedBuffer;



    const char inputString[] = "This is a test demo for RSA Implementation in Objective C";
    int len = strlen(inputString);
    // TODO: this is a hack since i know inputString length will be less than BUFFER_SIZE
    if (len > BUFFER_SIZE) len = BUFFER_SIZE-1;

    plainBuffer = (uint8_t *)calloc(BUFFER_SIZE, sizeof(uint8_t));
    cipherBuffer = (uint8_t *)calloc(CIPHER_BUFFER_SIZE, sizeof(uint8_t));
    decryptedBuffer = (uint8_t *)calloc(BUFFER_SIZE, sizeof(uint8_t));

    strncpy( (char *)plainBuffer, inputString, len);

    NSLog(@"init() plainBuffer: %s", plainBuffer);
    //NSLog(@"init(): sizeof(plainBuffer): %d", sizeof(plainBuffer));
    [self encryptWithPublicKey:(UInt8 *)plainBuffer cipherBuffer:cipherBuffer];
    NSLog(@"encrypted data: %s", cipherBuffer);
    //NSLog(@"init(): sizeof(cipherBuffer): %d", sizeof(cipherBuffer));
    [self decryptWithPrivateKey:cipherBuffer plainBuffer:decryptedBuffer];
    NSLog(@"decrypted data: %s", decryptedBuffer);
    //NSLog(@"init(): sizeof(decryptedBuffer): %d", sizeof(decryptedBuffer));
    NSLog(@"====== /second test =======================================");

    free(plainBuffer);
    free(cipherBuffer);
    free(decryptedBuffer);
}

/* Borrowed from:
 * https://developer.apple.com/library/mac/#documentation/security/conceptual/CertKeyTrustProgGuide/iPhone_Tasks/iPhone_Tasks.html
 */
- (void)encryptWithPublicKey:(uint8_t *)plainBuffer cipherBuffer:(uint8_t *)cipherBuffer
{

    NSLog(@"== encryptWithPublicKey()");

    OSStatus status = noErr;

    NSLog(@"** original plain text 0: %s", plainBuffer);

    size_t plainBufferSize = strlen((char *)plainBuffer);
    size_t cipherBufferSize = CIPHER_BUFFER_SIZE;

    NSLog(@"SecKeyGetBlockSize() public = %lu", SecKeyGetBlockSize([self getPublicKeyRef]));
    //  Error handling
    // Encrypt using the public.
    status = SecKeyEncrypt([self getPublicKeyRef],
                           PADDING,
                           plainBuffer,
                           plainBufferSize,
                           &cipherBuffer[0],
                           &cipherBufferSize
                           );
    NSLog(@"encryption result code: %ld (size: %lu)", status, cipherBufferSize);
    NSLog(@"encrypted text: %s", cipherBuffer);
}

- (void)decryptWithPrivateKey:(uint8_t *)cipherBuffer plainBuffer:(uint8_t *)plainBuffer
{
    OSStatus status = noErr;

    size_t cipherBufferSize = strlen((char *)cipherBuffer);

    NSLog(@"decryptWithPrivateKey: length of buffer: %lu", BUFFER_SIZE);
    NSLog(@"decryptWithPrivateKey: length of input: %lu", cipherBufferSize);

    // DECRYPTION
    size_t plainBufferSize = BUFFER_SIZE;

    //  Error handling
    status = SecKeyDecrypt([self getPrivateKeyRef],
                           PADDING,
                           &cipherBuffer[0],
                           cipherBufferSize,
                           &plainBuffer[0],
                           &plainBufferSize
                           );
    NSLog(@"decryption result code: %ld (size: %lu)", status, plainBufferSize);
    NSLog(@"FINAL decrypted text: %s", plainBuffer);

}



- (SecKeyRef)getPrivateKeyRef {
    OSStatus resultCode = noErr;
    SecKeyRef privateKeyReference = NULL;
//    NSData *privateTag = [NSData dataWithBytes:@"ABCD" length:strlen((const char *)@"ABCD")];
//    if(privateKey == NULL) {
        [self generateKeyPair:512];
        NSMutableDictionary * queryPrivateKey = [[NSMutableDictionary alloc] init];

        // Set the private key query dictionary.
        [queryPrivateKey setObject:(__bridge id)kSecClassKey forKey:(__bridge id)kSecClass];
        [queryPrivateKey setObject:privateTag forKey:(__bridge id)kSecAttrApplicationTag];
        [queryPrivateKey setObject:(__bridge id)kSecAttrKeyTypeRSA forKey:(__bridge id)kSecAttrKeyType];
        [queryPrivateKey setObject:[NSNumber numberWithBool:YES] forKey:(__bridge id)kSecReturnRef];

        // Get the key.
        resultCode = SecItemCopyMatching((__bridge CFDictionaryRef)queryPrivateKey, (CFTypeRef *)&privateKeyReference);
        NSLog(@"getPrivateKey: result code: %ld", resultCode);

        if(resultCode != noErr)
        {
            privateKeyReference = NULL;
        }

//        [queryPrivateKey release];
//    } else {
//        privateKeyReference = privateKey;
//    }

    return privateKeyReference;
}


#pragma mark - View lifecycle



- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    privateTag = [[NSData alloc] initWithBytes:privateKeyIdentifier length:sizeof(privateKeyIdentifier)];
    publicTag = [[NSData alloc] initWithBytes:publicKeyIdentifier length:sizeof(publicKeyIdentifier)];
    [self testAsymmetricEncryptionAndDecryption];

}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
}

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
}

- (void)viewDidDisappear:(BOOL)animated
{
    [super viewDidDisappear:animated];
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
        return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
    } else {
        return YES;
    }
}

- (void)generateKeyPair:(NSUInteger)keySize {
    OSStatus sanityCheck = noErr;
    publicKey = NULL;
    privateKey = NULL;

//  LOGGING_FACILITY1( keySize == 512 || keySize == 1024 || keySize == 2048, @"%d is an invalid and unsupported key size.", keySize );

    // First delete current keys.
//  [self deleteAsymmetricKeys];

    // Container dictionaries.
    NSMutableDictionary * privateKeyAttr = [[NSMutableDictionary alloc] init];
    NSMutableDictionary * publicKeyAttr = [[NSMutableDictionary alloc] init];
    NSMutableDictionary * keyPairAttr = [[NSMutableDictionary alloc] init];

    // Set top level dictionary for the keypair.
    [keyPairAttr setObject:(__bridge id)kSecAttrKeyTypeRSA forKey:(__bridge id)kSecAttrKeyType];
    [keyPairAttr setObject:[NSNumber numberWithUnsignedInteger:keySize] forKey:(__bridge id)kSecAttrKeySizeInBits];

    // Set the private key dictionary.
    [privateKeyAttr setObject:[NSNumber numberWithBool:YES] forKey:(__bridge id)kSecAttrIsPermanent];
    [privateKeyAttr setObject:privateTag forKey:(__bridge id)kSecAttrApplicationTag];
    // See SecKey.h to set other flag values.

    // Set the public key dictionary.
    [publicKeyAttr setObject:[NSNumber numberWithBool:YES] forKey:(__bridge id)kSecAttrIsPermanent];
    [publicKeyAttr setObject:publicTag forKey:(__bridge id)kSecAttrApplicationTag];
    // See SecKey.h to set other flag values.

    // Set attributes to top level dictionary.
    [keyPairAttr setObject:privateKeyAttr forKey:(__bridge id)kSecPrivateKeyAttrs];
    [keyPairAttr setObject:publicKeyAttr forKey:(__bridge id)kSecPublicKeyAttrs];

    // SecKeyGeneratePair returns the SecKeyRefs just for educational purposes.
    sanityCheck = SecKeyGeneratePair((__bridge CFDictionaryRef)keyPairAttr, &publicKey, &privateKey);
//  LOGGING_FACILITY( sanityCheck == noErr && publicKey != NULL && privateKey != NULL, @"Something really bad went wrong with generating the key pair." );
    if(sanityCheck == noErr  && publicKey != NULL && privateKey != NULL)
    {
        NSLog(@"Successful");
    }
//  [privateKeyAttr release];
//  [publicKeyAttr release];
//  [keyPairAttr release];
}


@end
以下是我最初发布答案的地方：

如果你需要更多的帮助，请告诉我

希望这有帮助。

这很酷！ 但是，我认为它不应该是UIViewController的子类，而是NSObject，我更改了它，它对我有效，它是：

注：所有工作均感谢@Parth Bath

经理

@interface RSAManager : NSObject
{
   SecKeyRef publicKey;
   SecKeyRef privateKey;
   NSData *publicTag;
   NSData *privateTag;
}

- (void)encryptWithPublicKey:(uint8_t *)plainBuffer cipherBuffer:(uint8_t *)cipherBuffer;
- (void)decryptWithPrivateKey:(uint8_t *)cipherBuffer plainBuffer:(uint8_t *)plainBuffer;
- (SecKeyRef)getPublicKeyRef;
- (SecKeyRef)getPrivateKeyRef;
- (void)testAsymmetricEncryptionAndDecryption;
- (void)generateKeyPair:(NSUInteger)keySize;

@end
经理

#import "RSAManager.h"

const size_t BUFFER_SIZE = 64;
const size_t CIPHER_BUFFER_SIZE = 1024;
const uint32_t PADDING = kSecPaddingNone;
static const UInt8 publicKeyIdentifier[] = "com.apple.sample.publickey";
static const UInt8 privateKeyIdentifier[] = "com.apple.sample.privatekey";

@implementation RSAManager

- (id)init
{
   self = [super init];

   if(self) {

      privateTag = [[NSData alloc] initWithBytes:privateKeyIdentifier length:sizeof(privateKeyIdentifier)];
      publicTag = [[NSData alloc] initWithBytes:publicKeyIdentifier length:sizeof(publicKeyIdentifier)];
      [self testAsymmetricEncryptionAndDecryption];
   }

   return self;
}

-(SecKeyRef)getPublicKeyRef {

   OSStatus sanityCheck = noErr;
   SecKeyRef publicKeyReference = NULL;

   if (publicKeyReference == NULL) {
      [self generateKeyPair:512];
      NSMutableDictionary *queryPublicKey = [[NSMutableDictionary alloc] init];

      // Set the public key query dictionary.
      [queryPublicKey setObject:(__bridge id)kSecClassKey forKey:(__bridge id)kSecClass];
      [queryPublicKey setObject:publicTag forKey:(__bridge id)kSecAttrApplicationTag];
      [queryPublicKey setObject:(__bridge id)kSecAttrKeyTypeRSA forKey:(__bridge id)kSecAttrKeyType];
      [queryPublicKey setObject:[NSNumber numberWithBool:YES] forKey:(__bridge id)kSecReturnRef];

      // Get the key.
      sanityCheck = SecItemCopyMatching((__bridge CFDictionaryRef)queryPublicKey, (CFTypeRef *)&publicKeyReference);


      if (sanityCheck != noErr)
      {
         publicKeyReference = NULL;
      }

      //        [queryPublicKey release];

   } else { publicKeyReference = publicKey; }

   return publicKeyReference;
}

- (void)testAsymmetricEncryptionAndDecryption {

   uint8_t *plainBuffer;
   uint8_t *cipherBuffer;
   uint8_t *decryptedBuffer;



   const char inputString[] = "This is a test demo for RSA Implementation in Objective C";
   int len = strlen(inputString);
   // TODO: this is a hack since i know inputString length will be less than BUFFER_SIZE
   if (len > BUFFER_SIZE) len = BUFFER_SIZE-1;

   plainBuffer = (uint8_t *)calloc(BUFFER_SIZE, sizeof(uint8_t));
   cipherBuffer = (uint8_t *)calloc(CIPHER_BUFFER_SIZE, sizeof(uint8_t));
   decryptedBuffer = (uint8_t *)calloc(BUFFER_SIZE, sizeof(uint8_t));

   strncpy( (char *)plainBuffer, inputString, len);

   NSLog(@"init() plainBuffer: %s", plainBuffer);
   //NSLog(@"init(): sizeof(plainBuffer): %d", sizeof(plainBuffer));
   [self encryptWithPublicKey:(UInt8 *)plainBuffer cipherBuffer:cipherBuffer];
   NSLog(@"encrypted data: %s", cipherBuffer);
   //NSLog(@"init(): sizeof(cipherBuffer): %d", sizeof(cipherBuffer));
   [self decryptWithPrivateKey:cipherBuffer plainBuffer:decryptedBuffer];
   NSLog(@"decrypted data: %s", decryptedBuffer);
   //NSLog(@"init(): sizeof(decryptedBuffer): %d", sizeof(decryptedBuffer));
   NSLog(@"====== /second test =======================================");

   free(plainBuffer);
   free(cipherBuffer);
   free(decryptedBuffer);
}

/* Borrowed from:
 * https://developer.apple.com/library/mac/#documentation/security/conceptual/CertKeyTrustProgGuide/iPhone_Tasks/iPhone_Tasks.html
 */
- (void)encryptWithPublicKey:(uint8_t *)plainBuffer cipherBuffer:(uint8_t *)cipherBuffer
{

   NSLog(@"== encryptWithPublicKey()");

   OSStatus status = noErr;

   NSLog(@"** original plain text 0: %s", plainBuffer);

   size_t plainBufferSize = strlen((char *)plainBuffer);
   size_t cipherBufferSize = CIPHER_BUFFER_SIZE;

   NSLog(@"SecKeyGetBlockSize() public = %lu", SecKeyGetBlockSize([self getPublicKeyRef]));
   //  Error handling
   // Encrypt using the public.
   status = SecKeyEncrypt([self getPublicKeyRef],
                          PADDING,
                          plainBuffer,
                          plainBufferSize,
                          &cipherBuffer[0],
                          &cipherBufferSize
                          );
   NSLog(@"encryption result code: %ld (size: %lu)", status, cipherBufferSize);
   NSLog(@"encrypted text: %s", cipherBuffer);
}

- (void)decryptWithPrivateKey:(uint8_t *)cipherBuffer plainBuffer:(uint8_t *)plainBuffer
{
   OSStatus status = noErr;

   size_t cipherBufferSize = strlen((char *)cipherBuffer);

   NSLog(@"decryptWithPrivateKey: length of buffer: %lu", BUFFER_SIZE);
   NSLog(@"decryptWithPrivateKey: length of input: %lu", cipherBufferSize);

   // DECRYPTION
   size_t plainBufferSize = BUFFER_SIZE;

   //  Error handling
   status = SecKeyDecrypt([self getPrivateKeyRef],
                          PADDING,
                          &cipherBuffer[0],
                          cipherBufferSize,
                          &plainBuffer[0],
                          &plainBufferSize
                          );
   NSLog(@"decryption result code: %ld (size: %lu)", status, plainBufferSize);
   NSLog(@"FINAL decrypted text: %s", plainBuffer);

}



- (SecKeyRef)getPrivateKeyRef {
   OSStatus resultCode = noErr;
   SecKeyRef privateKeyReference = NULL;
   //    NSData *privateTag = [NSData dataWithBytes:@"ABCD" length:strlen((const char *)@"ABCD")];
   //    if(privateKey == NULL) {
   [self generateKeyPair:512];
   NSMutableDictionary * queryPrivateKey = [[NSMutableDictionary alloc] init];

   // Set the private key query dictionary.
   [queryPrivateKey setObject:(__bridge id)kSecClassKey forKey:(__bridge id)kSecClass];
   [queryPrivateKey setObject:privateTag forKey:(__bridge id)kSecAttrApplicationTag];
   [queryPrivateKey setObject:(__bridge id)kSecAttrKeyTypeRSA forKey:(__bridge id)kSecAttrKeyType];
   [queryPrivateKey setObject:[NSNumber numberWithBool:YES] forKey:(__bridge id)kSecReturnRef];

   // Get the key.
   resultCode = SecItemCopyMatching((__bridge CFDictionaryRef)queryPrivateKey, (CFTypeRef *)&privateKeyReference);
   NSLog(@"getPrivateKey: result code: %ld", resultCode);

   if(resultCode != noErr)
   {
      privateKeyReference = NULL;
   }

   //        [queryPrivateKey release];
   //    } else {
   //        privateKeyReference = privateKey;
   //    }

   return privateKeyReference;
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
   // Return YES for supported orientations
   if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
      return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
   } else {
      return YES;
   }
}

- (void)generateKeyPair:(NSUInteger)keySize {
   OSStatus sanityCheck = noErr;
   publicKey = NULL;
   privateKey = NULL;

   //  LOGGING_FACILITY1( keySize == 512 || keySize == 1024 || keySize == 2048, @"%d is an invalid and unsupported key size.", keySize );

   // First delete current keys.
   //  [self deleteAsymmetricKeys];

   // Container dictionaries.
   NSMutableDictionary * privateKeyAttr = [[NSMutableDictionary alloc] init];
   NSMutableDictionary * publicKeyAttr = [[NSMutableDictionary alloc] init];
   NSMutableDictionary * keyPairAttr = [[NSMutableDictionary alloc] init];

   // Set top level dictionary for the keypair.
   [keyPairAttr setObject:(__bridge id)kSecAttrKeyTypeRSA forKey:(__bridge id)kSecAttrKeyType];
   [keyPairAttr setObject:[NSNumber numberWithUnsignedInteger:keySize] forKey:(__bridge id)kSecAttrKeySizeInBits];

   // Set the private key dictionary.
   [privateKeyAttr setObject:[NSNumber numberWithBool:YES] forKey:(__bridge id)kSecAttrIsPermanent];
   [privateKeyAttr setObject:privateTag forKey:(__bridge id)kSecAttrApplicationTag];
   // See SecKey.h to set other flag values.

   // Set the public key dictionary.
   [publicKeyAttr setObject:[NSNumber numberWithBool:YES] forKey:(__bridge id)kSecAttrIsPermanent];
   [publicKeyAttr setObject:publicTag forKey:(__bridge id)kSecAttrApplicationTag];
   // See SecKey.h to set other flag values.

   // Set attributes to top level dictionary.
   [keyPairAttr setObject:privateKeyAttr forKey:(__bridge id)kSecPrivateKeyAttrs];
   [keyPairAttr setObject:publicKeyAttr forKey:(__bridge id)kSecPublicKeyAttrs];

   // SecKeyGeneratePair returns the SecKeyRefs just for educational purposes.
   sanityCheck = SecKeyGeneratePair((__bridge CFDictionaryRef)keyPairAttr, &publicKey, &privateKey);
   //  LOGGING_FACILITY( sanityCheck == noErr && publicKey != NULL && privateKey != NULL, @"Something really bad went wrong with generating the key pair." );
   if(sanityCheck == noErr  && publicKey != NULL && privateKey != NULL)
   {
      NSLog(@"Successful");
   }
   //  [privateKeyAttr release];
   //  [publicKeyAttr release];
   //  [keyPairAttr release];
}

@end
亲爱的Parth Bhatt，非常感谢您的帮助，但我没有看到要以文本形式解密的加密数据。@ParthHatt您找到导出私钥的方法了吗？我试图在iphone上加密文本，在服务器端解密。但我无法导出私钥的模数和指数（或任何格式）。@ParthBhatt我得到的错误与AmirIphone得到的错误相同。。。你有什么解决办法吗。。谢谢-我的加密文本是-4；è»–vJNØmYú：º‰aé-™-›qS•？]~OÍ™vIá%sj…◊就像这样。。但是我需要Base64文本如何加密超过64个字符的字符串。我有一个800个字符的字符串。我有一个带密码的公钥（.pem）；如何使用上面的代码？我希望你能帮助我这个可能的副本。缓冲区大小是多少？我需要能够加密/解密20-100KB的文本。使用you方法，我只加密/解密前64个字符。你能再解释一下吗，或者给我指出正确的方向，这样我就可以了解它了。你通常用对称算法（如AES）和随机密钥加密数据，然后用RSA加密AES密钥。我在
encryptWithPublicKey:cipherBuffer:
的NSLog（@“SecKeyGetBlockSize（）public=%lu”）中获得了一个EXC坏访问权限，SecKeyGetBlockSize（[self-getPublicKeyRef]）因为
getPublicKeyRef
返回nil//获取此数据时，我希望密钥采用base64编码形式