How to sign a string with Private Key

Question

Hi, I need help. I have been searching for a solution for past few days to no avail. As per the subject, I need to sign a string with private key and SHA256.

1) I had created a Bridging Header file and in it, i include the code

#import <CommonCrypto/CommonHMAC.h>

#import <CommonCrypto/CommonDigest.h>

2) Have added the path in the Build setting : Project-name/Project-name-Bridging-header.h

3) I used below code on Xcode 8 with Swift3 and I encountered below error messages base on below function :signString

//- Error Msg 1 : use of unresolved identifier 'CC_SHA256_DIGEST_LENGTH'

//- Error Msg 2: Use of unresolved identifier 'CC_SHA256

//- Error Msg 3: Use of unresolved identifier 'CC_LONG'

func signString(string: String, privateKey: SecKey) -> NSData? {

//-1: Error Msg : use of unresolved identifier 'CC_SHA256_DIGEST_LENGTH'

let digest = NSMutableData(length: Int(CC_SHA256_DIGEST_LENGTH))!

let stringData: NSData = string.data(using: String.Encoding.utf8)! NSData

//-2: Error Msg : Use of unresolved identifier 'CC_SHA256

//-3: Error Msg : Use of unresolved identifier 'CC_LONG'

CC_SHA256(stringData.bytes, CC_LONG(stringData.length), UnsafeMutablePointer<UInt8>(digest.mutableBytes))

let signedData: NSMutableData = NSMutableData(length: SecKeyGetBlockSize(privateKey))!

var signedDataLength: Int = signedData.length

let err: OSStatus = SecKeyRawSign(

privateKey,

SecPadding.PKCS1SHA256,

UnsafePointer<UInt8>(digest.bytes),

digest.length,

UnsafeMutablePointer<UInt8>(signedData.mutableBytes),

&signedDataLength

)

switch err {

case noErr:

return signedData

default:

return nil

}

Can you help me to correct the code below. your help is much appreciated.

Thanks

2.7k

Posted by

SkyWire

Reply

Add a Comment

Answer 1

I suppose you have looked at this post :

h ttps://stackoverflow.com/questions/35749197/how-to-use-common-crypto-and-or-calculate-sha256-in-swift-2-3

There's an interesting commnt on how toc create the bridging header (which I never had to do in my apps, so don't know how much relevant it is).

to add bridging header, I just add a new

Objective-C

file in Swift project, if it's a first Objc file then it will ask whether or not you want to add a bridging header. Yes, then go back to remove that Objc file.

Hope it helps.

Posted by

Claude31

Add a Comment

Answer 2

Hi Claude31,

Thanks for the link. I still dont know how to solve the problem.

for the link you provided:

//swift 3

guard let messageData = string.data(using:String.Encoding.utf8) else { return nil }
var digestData = Data(count: Int(CC_SHA256_DIGEST_LENGTH))

_ = digestData.withUnsafeMutableBytes {digestBytes in
messageData.withUnsafeBytes {messageBytes in
CC_SHA256(messageBytes, CC_LONG(messageData.count), digestBytes)
}
}

How to use this (disgestData) into SecKeyRawSign() ?

is it replacing this line: UnsafePointer<UInt8>(digest.bytes)

let signedData: NSMutableData = NSMutableData(length: SecKeyGetBlockSize(privateKey))!

var signedDataLength: Int = signedData.length

let err: OSStatus = SecKeyRawSign(

privateKey,
SecPadding.PKCS1SHA256,
UnsafePointer<UInt8>(digest.bytes),
digest.length,
UnsafeMutablePointer<UInt8>(signedData.mutableBytes),
&signedDataLength

)

How I will use the swift3 code above into this

func signString(string: String, privateKey: SecKey) -> NSData? { }

Thanks

Posted by

SkyWire

Add a Comment

Answer 3

Can any1 correct my code as it now not workable.

Thanks

Posted by

SkyWire

Add a Comment

Answer 4

Hope this will help.

h ttps://codereview.stackexchange.com/questions/139698/signing-a-string-using-an-identity-and-trust-from-a-pkcs-12-bundle

I found this part interesting:

    var signedBytesSize: size_t = SecKeyGetBlockSize(privateKey)
    var signedBytes = [UInt8](count: signedBytesSize, repeatedValue: 0)
    // Sign data
    let requestorData = requestorID.dataUsingEncoding(NSUTF8StringEncoding)!
    // Generate a digital signature for our requestor from our cert
    status = SecKeyRawSign(privateKey, .PKCS1, UnsafePointer(requestorData.bytes),
                                   requestorData.length, &signedBytes, &signedBytesSize)

Posted by

Claude31

Add a Comment

How to sign a string with Private Key

Replies