Add function to compute MD5 from certificate

TunnelKit.xcodeproj/project.pbxproj

@@ -45,6 +45,7 @@
 		0E3E0F212108A8CC00B371C1 /* SessionProxy+PushReply.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0E3E0F202108A8CC00B371C1 /* SessionProxy+PushReply.swift */; };
 		0E3E0F222108A8CC00B371C1 /* SessionProxy+PushReply.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0E3E0F202108A8CC00B371C1 /* SessionProxy+PushReply.swift */; };
 		0E58F1302138AC2F00A49F27 /* DNSTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0E58F12F2138AC2F00A49F27 /* DNSTests.swift */; };
+		0E749F622178911D00BB2701 /* pia-2048.pem in Resources */ = {isa = PBXBuildFile; fileRef = 0E749F612178911C00BB2701 /* pia-2048.pem */; };
 		0E85A25A202CC5AF0059E9F9 /* AppExtensionTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0E85A259202CC5AE0059E9F9 /* AppExtensionTests.swift */; };
 		0E9379C91F819A4300CE91B6 /* TunnelKit.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 0E17D7F91F730D9F009EE129 /* TunnelKit.framework */; };
 		0EB2B45320F0BB44004233D7 /* EncryptionTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0EB2B45220F0BB44004233D7 /* EncryptionTests.swift */; };
@@ -214,6 +215,7 @@
 		0E58F12F2138AC2F00A49F27 /* DNSTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = DNSTests.swift; sourceTree = "<group>"; };
 		0E6479DD212EAC96008E6888 /* Info.plist */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.plist.xml; path = Info.plist; sourceTree = "<group>"; };
 		0E6479E0212EACD6008E6888 /* Info.plist */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.plist.xml; path = Info.plist; sourceTree = "<group>"; };
+		0E749F612178911C00BB2701 /* pia-2048.pem */ = {isa = PBXFileReference; lastKnownFileType = text; path = "pia-2048.pem"; sourceTree = "<group>"; };
 		0E85A259202CC5AE0059E9F9 /* AppExtensionTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = AppExtensionTests.swift; sourceTree = "<group>"; };
 		0E85A25B202CCA3D0059E9F9 /* TunnelKitHost.entitlements */ = {isa = PBXFileReference; lastKnownFileType = text.plist.entitlements; path = TunnelKitHost.entitlements; sourceTree = "<group>"; };
 		0EB2B45220F0BB44004233D7 /* EncryptionTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = EncryptionTests.swift; sourceTree = "<group>"; };
@@ -340,6 +342,7 @@
 				0EB2B45620F0BD16004233D7 /* RandomTests.swift */,
 				0EB2B45C20F0BF41004233D7 /* RawPerformanceTests.swift */,
 				0EB2B45A20F0BE4C004233D7 /* TestUtils.swift */,
+				0E749F612178911C00BB2701 /* pia-2048.pem */,
 			);
 			path = TunnelKitTests;
 			sourceTree = "<group>";
@@ -719,6 +722,7 @@
 			isa = PBXResourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				0E749F622178911D00BB2701 /* pia-2048.pem in Resources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};

TunnelKit/Sources/Core/TLSBox.h

@@ -51,6 +51,8 @@ extern NSString *const TLSBoxPeerVerificationErrorNotification;
 //
 @interface TLSBox : NSObject
 
++ (NSString *)md5ForCertificatePath:(NSString *)path;
+
 - (instancetype)initWithCAPath:(NSString *)caPath
          clientCertificatePath:(nullable NSString *)clientCertificatePath
                  clientKeyPath:(nullable NSString *)clientKeyPath;

TunnelKit/Sources/Core/TLSBox.m

@@ -75,6 +75,25 @@ int TLSBoxVerifyPeer(int ok, X509_STORE_CTX *ctx) {
 
 @implementation TLSBox
 
++ (NSString *)md5ForCertificatePath:(NSString *)path
+{
+    const EVP_MD *alg = EVP_get_digestbyname("MD5");
+    uint8_t md[16];
+    unsigned int len;
+
+    FILE *pem = fopen([path cStringUsingEncoding:NSASCIIStringEncoding], "r");
+    X509 *cert = PEM_read_X509(pem, NULL, NULL, NULL);
+    X509_digest(cert, alg, md, &len);
+    X509_free(cert);
+    NSCAssert2(len == sizeof(md), @"Unexpected MD5 size (%d != %lu)", len, sizeof(md));
+
+    NSMutableString *hex = [[NSMutableString alloc] initWithCapacity:2 * sizeof(md)];
+    for (int i = 0; i < sizeof(md); ++i) {
+        [hex appendFormat:@"%02x", md[i]];
+    }
+    return hex;
+}
+
 - (instancetype)init
 {
     [NSException raise:NSInvalidArgumentException format:@"Use initWithCAPath:clientCertificatePath:clientKeyPath:"];

TunnelKitTests/EncryptionTests.swift

@@ -86,6 +86,14 @@ class EncryptionTests: XCTestCase {
         let decrypted = try! server.decrypter().decryptData(encrypted, extra: extra)
         XCTAssertEqual(plain, decrypted)
     }
+    
+    func testCertificateMD5() {
+        let path = Bundle(for: EncryptionTests.self).path(forResource: "pia-2048", ofType: "pem")!
+        let md5 = TLSBox.md5(forCertificatePath: path)
+        let exp = "e2fccccaba712ccc68449b1c56427ac1"
+        print(md5)
+        XCTAssertEqual(md5, exp)
+    }
 
     private func clientServer(_ c: String?, _ d: String?) -> (CryptoBox, CryptoBox) {
         let client = CryptoBox(cipherAlgorithm: c, digestAlgorithm: d)

TunnelKitTests/pia-2048.pem

@@ -0,0 +1,34 @@
+-----BEGIN CERTIFICATE-----
+MIIFqzCCBJOgAwIBAgIJAKZ7D5Yv87qDMA0GCSqGSIb3DQEBDQUAMIHoMQswCQYD
+VQQGEwJVUzELMAkGA1UECBMCQ0ExEzARBgNVBAcTCkxvc0FuZ2VsZXMxIDAeBgNV
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+-----END CERTIFICATE-----
+