Digitally sign a pdf

[ferencIOS]

Hello to all.
as the title suggests I'm trying to figure out how to digitally sign a pdf. In the iOS documentation I did not find anything that can help me.
The alternatives I have are OpenSSL (too complex, I'm not a C / C ++ developer), BouncyCastle (unfortunately only java or C #).

Reading the code, it looks like Shield can help me.

These are code snippets from my colleagues on Android:

import org.bouncycastle.asn1.x509.AlgorithmIdentifier
import org.bouncycastle.crypto.Digest
import org.bouncycastle.crypto.Signer
import org.bouncycastle.operator.bc.BcContentSignerBuilder

internal class ContentSignerBuilder(
    val sigAlgId: AlgorithmIdentifier,
    val digAlgId: AlgorithmIdentifier
) : BcContentSignerBuilder(sigAlgId, digAlgId) {

    var digestSigner: DigestSigner? = null

    override fun createSigner(sigAlgId: AlgorithmIdentifier, digAlgId: AlgorithmIdentifier): Signer {
        val digest: Digest = digestProvider.get(digAlgId)
        digestSigner = DigestSigner(
            digest = digest
        )

        return digestSigner!!
    }

}

where DigestSigner

import org.bouncycastle.crypto.*


internal class DigestSigner(
    val digest: Digest
) : Signer {

    var byteToSign: ByteArray? = null
    var signedBytes: ByteArray? = null

    override fun init(forSigning: Boolean, param: CipherParameters?) {
        if(byteToSign == null)
            reset()
    }

    override fun update(b: Byte) {
        if(byteToSign !== null)
            digest.update(b)
    }

    override fun update(b: ByteArray?, off: Int, len: Int) {
        if(byteToSign == null)
            digest.update(b, off, len)
    }

    override fun generateSignature(): ByteArray {
        if(signedBytes != null && signedBytes!!.isNotEmpty()) {
            return signedBytes as ByteArray
        }

        val hash = ByteArray(digest.digestSize)
        digest.doFinal(hash, 0)

        byteToSign = hash
        return hash
    }

    override fun verifySignature(signature: ByteArray?): Boolean {
        throw IllegalStateException(DigestSigner::class.java.simpleName + ": verifySignature not supported");
    }

    override fun reset() {
        digest.reset()
    }

    @Throws(CryptoException::class, DataLengthException::class)
    fun getHashToSign(): ByteArray? {
        return byteToSign
    }
}

I would understand if Shield is able to do the same things as BouncyCastle.
And above all, how can I make them happen.

Thanks in advance!

[kdubb]

You can generate a signature with a key using SecKey.sign & verify it using SecKey.verify. Note that these are now just convenience functions for Apple's security functions SecKeyCreateSignature & SecKeyVerifySignature; Shield isn't really needed for that.