Importing CommonCrypto in a Swift framework

Question

How do you import CommonCrypto in a Swift framework for iOS?

I understand how to use CommonCrypto in a Swift app: You add #import <CommonCrypto/CommonCrypto.h> to the bridging header. However, Swift frameworks don't support bridging headers. The documentation says:

You can import external frameworks that have a pure Objective-C codebase, a pure Swift codebase, or a mixed-language codebase. The process for importing an external framework is the same whether the framework is written in a single language or contains files from both languages. When you import an external framework, make sure the Defines Module build setting for the framework you’re importing is set to Yes.

You can import a framework into any Swift file within a different target using the following syntax:

import FrameworkName

Unfortunately, import CommonCrypto doesn't work. Neither does adding #import <CommonCrypto/CommonCrypto.h> to the umbrella header.

Answer 1

I'm not sure if something's changed with Xcode 9.2 but it's now much simpler to achieve this. The only things I had to do are create a folder called "CommonCrypto" in my framework project directory and create two files inside it, one called "cc.h" as follows:

#include <CommonCrypto/CommonCrypto.h>
#include <CommonCrypto/CommonRandom.h>

And another called module.modulemap:

module CommonCrypto {
    export *
    header "cc.h"
}

(I don't know why you can't reference header files from the SDKROOT area directly in a modulemap file but I couldn't get it to work)

The third thing is to find the "Import Paths" setting and set to $(SRCROOT). In fact you can set it to whatever folder you want the CommonCrypto folder to be under, if you don't want it at the root level.

After this you should be able to use

import CommonCrypto

In any swift file and all the types/functions/etc. are available.

A word of warning though - if your app uses libCommonCrypto (or libcoreCrypto) it's exceptionally easy for a not-too-sophisticated hacker to attach a debugger to your app and find out what keys are being passed to these functions.

Answer 2

I found a GitHub project that successfully uses CommonCrypto in a Swift framework: SHA256-Swift. Also, this article about the same problem with sqlite3 was useful.

Based on the above, the steps are:

1) Create a CommonCrypto directory inside the project directory. Within, create a module.map file. The module map will allow us to use the CommonCrypto library as a module within Swift. Its contents are:

module CommonCrypto [system] {
    header "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator8.0.sdk/usr/include/CommonCrypto/CommonCrypto.h"
    link "CommonCrypto"
    export *
}

2) In Build Settings, within Swift Compiler - Search Paths, add the CommonCrypto directory to Import Paths (SWIFT_INCLUDE_PATHS).

3) Finally, import CommonCrypto inside your Swift files as any other modules. For example:

import CommonCrypto

extension String {

    func hnk_MD5String() -> String {
        if let data = self.dataUsingEncoding(NSUTF8StringEncoding)
        {
            let result = NSMutableData(length: Int(CC_MD5_DIGEST_LENGTH))
            let resultBytes = UnsafeMutablePointer<CUnsignedChar>(result.mutableBytes)
            CC_MD5(data.bytes, CC_LONG(data.length), resultBytes)
            let resultEnumerator = UnsafeBufferPointer<CUnsignedChar>(start: resultBytes, length: result.length)
            let MD5 = NSMutableString()
            for c in resultEnumerator {
                MD5.appendFormat("%02x", c)
            }
            return MD5
        }
        return ""
    }
}

Limitations

Using the custom framework in another project fails at compile time with the error missing required module 'CommonCrypto'. This is because the CommonCrypto module does not appear to be included with the custom framework. A workaround is to repeat step 2 (setting Import Paths) in the project that uses the framework.

The module map is not platform independent (it currently points to a specific platform, the iOS 8 Simulator). I don't know how to make the header path relative to the current platform.

Updates for iOS 8 <= We should remove the line link "CommonCrypto", to get the successful compilation.

UPDATE / EDIT

I kept getting the following build error:

ld: library not found for -lCommonCrypto for architecture x86_64 clang: error: linker command failed with exit code 1 (use -v to see invocation)

Unless I removed the line link "CommonCrypto" from the module.map file I created. Once I removed this line it built ok.

Answer 3

The modulemap solutions can be good, and are robust against SDK changes, but I've found them awkward to use in practice, and not as reliable as I'd like when handing things out to others. To try to make it all more foolproof, I went a different way:

Just copy the headers.

I know, fragile. But Apple almost never makes significant changes to CommonCrypto and I'm living the dream that they will not change it in any significant way without also finally making CommonCrypto a modular header.

By "copy the headers" I mean "cut and paste all of the headers you need into one massive header in your project just like the preprocessor would do." As an example of this that you can copy or adapt, see RNCryptor.h.

Note that all of these files are licensed under APSL 2.0, and this approach intentionally maintains the copyright and license notices. My concatenation step is licensed under MIT, and that only applies up to the next license notice).

I am not saying this is a beautiful solution, but so far it seems to have been an incredibly simple solution to both implement and support.

Answer 4

WARNING: iTunesConnect may reject apps that are using this method.

---

New member on my team accidentally broke the solution given by one of the top answers, so I decided to consolidate it in a small wrapper project called CommonCryptoModule. You can install it manually or via Cocoapods:

pod 'CommonCryptoModule', '~> 1.0.2'

Then, all you have to do is to import the module where you need CommonCrypto, like so:

import CommonCryptoModule

Hope someone else finds this useful.

Answer 5

Something a little simpler and more robust is to create an Aggregate target called "CommonCryptoModuleMap" with a Run Script phase to generate the module map automatically and with the correct Xcode/SDK path:

The Run Script phase should contain this bash:

# This if-statement means we'll only run the main script if the CommonCryptoModuleMap directory doesn't exist
# Because otherwise the rest of the script causes a full recompile for anything where CommonCrypto is a dependency
# Do a "Clean Build Folder" to remove this directory and trigger the rest of the script to run
if [ -d "${BUILT_PRODUCTS_DIR}/CommonCryptoModuleMap" ]; then
    echo "${BUILT_PRODUCTS_DIR}/CommonCryptoModuleMap directory already exists, so skipping the rest of the script."
    exit 0
fi

mkdir -p "${BUILT_PRODUCTS_DIR}/CommonCryptoModuleMap"
cat <<EOF > "${BUILT_PRODUCTS_DIR}/CommonCryptoModuleMap/module.modulemap"
module CommonCrypto [system] {
    header "${SDKROOT}/usr/include/CommonCrypto/CommonCrypto.h"
    export *
}
EOF

Using shell code and ${SDKROOT} means you don't have to hard code the Xcode.app path which can vary system-to-system, especially if you use xcode-select to switch to a beta version, or are building on a CI server where multiple versions are installed in non-standard locations. You also don't need to hard code the SDK so this should work for iOS, macOS, etc. You also don't need to have anything sitting in your project's source directory.

After creating this target, make your library/framework depend on it with a Target Dependencies item:

This will ensure the module map is generated before your framework is built.

macOS note: If you're supporting macOS as well, you'll need to add macosx to the Supported Platforms build setting on the new aggregate target you just created, otherwise it won't put the module map in the correct Debug derived data folder with the rest of the framework products.

Next, add the module map's parent directory, ${BUILT_PRODUCTS_DIR}/CommonCryptoModuleMap, to the "Import Paths" build setting under the Swift section (SWIFT_INCLUDE_PATHS):

Remember to add a $(inherited) line if you have search paths defined at the project or xcconfig level.

That's it, you should now be able to import CommonCrypto

Update for Xcode 10

Xcode 10 now ships with a CommonCrypto module map making this workaround unnecessary. If you would like to support both Xcode 9 and 10 you can do a check in the Run Script phase to see if the module map exists or not, e.g.

COMMON_CRYPTO_DIR="${SDKROOT}/usr/include/CommonCrypto"
if [ -f "${COMMON_CRYPTO_DIR}/module.modulemap" ]
then
   echo "CommonCrypto already exists, skipping"
else
    # generate the module map, using the original code above
fi

Answer 6

If are here for the hashing algorithms, like SHA, MD5 etc, don't use the bulky CommonCrypto library. Find the specific hashing library you are looking for instead.

For example, for MD5, you can go with SwiftHash