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Reading Files

To make file access easier, the security transforms API provides read transforms that return the contents of a file in a CFData object. By chaining this transform with other transforms, you can effectively use a readable file stream as input to any other transform.

To create a read transform object

If you do not already have a read stream, create or obtain a CFURLRef object for the source file.
For example, to read the file encrypt2_key in the current working directory, you could write code like the following:
CFURLRef url = CFURLCreateFromFileSystemRepresentation (
kCFAllocatorDefault,
"encrypt2_key",
12,
false);

If you do not already have a read stream, create a CFReadStreamRef object from that CFURLRef.

For example:

    CFReadStreamRef cfrs = CFReadStreamCreateWithFile(

                                kCFAllocatorDefault,

                                url);

Call SecTransformCreateReadTransformWithReadStream to create the read transform.

For example:

    SecTransformRef readTransform = SecTransformCreateReadTransformWithReadStream(cfrs);

If your encryption key is a series of raw bytes, you can now get the contents of a file as a CFData object by calling SecTransformExecute or SecTransformExecuteAsync on the transform object as follows:

CFDataRef cfdatacryptokey = SecTransformExecute(readTransform, &error);

If your encryption key is in Base64 encoding, you may find it useful to group this transform with a Base64 decoder object. For example:

    /* Create the Base64 encoder object. */

    SecTransformRef decoder = SecDecodeTransformCreate(kSecBase64Encoding, &error);

    if (error) { CFShow(error); exit(-1); }

    /* Create the group transform object. */

    SecGroupTransformRef group = SecTransformCreateGroupTransform();

    /* Connect the output of the read transform

       to the input of the decoder using the

       group transform object. */

    SecTransformConnectTransforms(readTransform, kSecTransformOutputAttributeName,

        decoder, kSecTransformInputAttributeName, group, &error);

    /* Perform the group transform. */

    CFDataRef cfdatacryptokey = SecTransformExecute(group, &error);

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