add function and tests to convert public key to public key hash

Sources/KukaiCryptoSwift/KeyPair.swift

@@ -22,6 +22,14 @@ public enum EllipticalCurve: String, Codable {
 		else if prefix == "tz2" { return .secp256k1 }
 		else { return nil }
 	}
+
+	public static func fromBase58Key(_ key: String) -> EllipticalCurve? {
+		let prefix = key.lowercased().prefix(4)
+
+		if prefix == "edpk" { return .ed25519 }
+		else if prefix == "sppk" { return .secp256k1 }
+		else { return nil }
+	}
 }
 
 /// A struct representing a both a `PrivateKey` and `PublicKey` with helper methods to create various kinds

Sources/KukaiCryptoSwift/PublicKey.swift

@@ -92,6 +92,25 @@ public struct PublicKey: Codable {
 				return secp256k1_ecdsa_verify(context, &cSignature, message, &publicKey) == 1
 		}
 	}
+
+	/**
+	 Take a base58Encoded public key (with a prefix) and convert it to a tzX public key hash
+	 */
+	public static func publicKeyHash(fromBase58EncodedKey key: String) -> String? {
+		guard let algo = EllipticalCurve.fromBase58Key(key),
+			  let decoded = Base58Check.decode(string: key, prefix: algo == .ed25519 ? Prefix.Keys.Ed25519.public : Prefix.Keys.Secp256k1.public),
+			  let hash = Sodium.shared.genericHash.hash(message: decoded, outputLength: 20) else {
+			return nil
+		}
+
+		switch algo {
+			case .ed25519:
+				return Base58Check.encode(message: hash, prefix: Prefix.Address.tz1)
+
+			case .secp256k1:
+				return Base58Check.encode(message: hash, prefix: Prefix.Address.tz2)
+		}
+	}
 }
 
 extension PublicKey: CustomStringConvertible {

Tests/KukaiCryptoSwiftTests/KeyPairTests.swift

@@ -175,4 +175,18 @@ final class KeyPairTests: XCTestCase {
 		let pubKeySafety = KeyPair.secp256k1PublicKey(fromPrivateKeyBytes: signatureBytes)
 		XCTAssert(pubKeySafety == nil, (pubKeySafety?.bytes.count ?? 0).description)
 	}
+
+	func testKeyToHash() throws {
+		let hash1 = PublicKey.publicKeyHash(fromBase58EncodedKey: "edpkuLshcvrn2x7c2QtCCMv8XFNEM2gHkPDGb3paKt2hBvnBRfepR4")
+		XCTAssert(hash1 == "tz1Xx4vxaUCkgxfaUhr1EV1kvTE2Rt3BkEdm", hash1 ?? "-")
+
+		let hash2 = PublicKey.publicKeyHash(fromBase58EncodedKey: "edpkuaUnRZQzwP1QYHFFXzbhN919wg17KHm7vHH86pxxgSSkqT7U4a")
+		XCTAssert(hash2 == "tz1ZYoRJ2iouRi5r6CT83Ptp9Bof7RMRkxXe", hash2 ?? "-")
+
+		let hash3 = PublicKey.publicKeyHash(fromBase58EncodedKey: "edpkufQ3nNdMJBkgfzCgCLmk1tbfLsqK7W8AR37KiCe7tDVvmsroHh")
+		XCTAssert(hash3 == "tz1WCBJKr1rRivyCnN9hREpRAMqrLdmqDcym", hash3 ?? "-")
+
+		let hash4 = PublicKey.publicKeyHash(fromBase58EncodedKey: "sppk7Zzqz2AjP4yXqr5ys99gZkaPLFKfGKnUxn3u1T1xfNSArZ5CKX6")
+		XCTAssert(hash4 == "tz2HpbGQcmU3UyusJ78Sbqeg9fYteamSMDGo", hash4 ?? "-")
+	}
 }