[iphone] Convert NSData to String?

I am storing a openssl private Key EVP_PKEY as nsdata. For this I am serializing into a byte stream using the code below

unsigned char *buf, *p;
int len;
len = i2d_PrivateKey(pkey, NULL);
buf = OPENSSL_malloc(len); 
p = buf;
i2d_PrivateKey(pkey, &p);

where pkey is of type EVP_PKEY. Then I am storing the bytes from buffer 'p' as an NSData using the line given below

NSData *keydata = [NSData dataWithBytes:P length:len];

Now I am converting it to a NSString using the code given below but when i print it into console its giving some other characters.

NSString *content =[ NSString stringWithCString:[keydata bytes] encoding:NSUTF8StringEncoding];

Could someone help?

Basically I want to store the EVP_PKEY into a sqlite database

am I on the right track? Thanks.

Prior Swift 3.0 :

String(data: yourData, encoding: NSUTF8StringEncoding)

For Swift 4.0:

String(data: yourData, encoding: .utf8)

I believe your "P" as the dataWithBytes param

NSData *keydata = [NSData dataWithBytes:P length:len];

should be "buf"

NSData *keydata = [NSData dataWithBytes:buf length:len];

since i2d_PrivateKey puts the pointer to the output buffer p at the end of the buffer and waiting for further input, and buf is still pointing to the beginning of your buffer.

The following code works for me where pkey is a pointer to an EVP_PKEY:

unsigned char *buf, *pp;
int len = i2d_PrivateKey(pkey, NULL);
buf = OPENSSL_malloc(len); 
pp = buf;
i2d_PrivateKey(pkey, &pp);

NSData* pkeyData = [NSData dataWithBytes:(const void *)buf length:len];
DLog(@"Private key in hex (%d): %@", len, pkeyData);

You can use an online converter to convert your binary data into base 64 (http://tomeko.net/online_tools/hex_to_base64.php?lang=en) and compare it to the private key in your cert file after using the following command and checking the output of mypkey.pem:

openssl pkcs12 -in myCert.p12 -nocerts -nodes -out mypkey.pem

I referenced your question and this EVP function site for my answer.

Swift 3:

String(data: data, encoding: .utf8)

Swift 5:

String(data: data!, encoding: String.Encoding.utf8)

A simple way to convert arbitrary NSData to NSString is to base64 encode it.

NSString *base64EncodedKey = [keydata base64EncodedStringWithOptions: NSDataBase64Encoding64CharacterLineLength];

You can then store it into your database for reuse later. Just decode it back to NSData.