1+ package com .yubico .webauthn ;
2+
3+ import com .fasterxml .jackson .databind .JsonNode ;
4+ import com .yubico .internal .util .ExceptionUtil ;
5+ import com .yubico .webauthn .data .AttestationObject ;
6+ import com .yubico .webauthn .data .AttestationType ;
7+ import com .yubico .webauthn .data .ByteArray ;
8+ import java .nio .charset .Charset ;
9+ import java .io .IOException ;
10+ import javax .net .ssl .SSLException ;
11+ import java .security .GeneralSecurityException ;
12+ import java .security .cert .X509Certificate ;
13+ import java .util .Arrays ;
14+ import java .util .Optional ;
15+ import java .util .ArrayList ;
16+ import java .util .List ;
17+ import lombok .extern .slf4j .Slf4j ;
18+ import com .google .api .client .json .webtoken .JsonWebSignature ;
19+ import com .google .api .client .json .jackson2 .JacksonFactory ;
20+ import org .apache .http .conn .ssl .DefaultHostnameVerifier ;
21+
22+ @ Slf4j
23+ class AndroidSafetynetAttestationStatementVerifier implements AttestationStatementVerifier {
24+
25+ private final BouncyCastleCrypto crypto = new BouncyCastleCrypto ();
26+
27+ private static final DefaultHostnameVerifier HOSTNAME_VERIFIER = new DefaultHostnameVerifier ();
28+
29+ private X509Certificate mX5cCert = null ;
30+
31+ public Optional <List <X509Certificate >> getAttestationTrustPath () {
32+ if (mX5cCert != null ) {
33+ List <X509Certificate > certs = new ArrayList <>(1 );
34+ certs .add (mX5cCert );
35+ return Optional .of (certs );
36+ }
37+ return Optional .empty ();
38+ }
39+
40+ @ Override
41+ public AttestationType getAttestationType (AttestationObject attestation ) {
42+ return AttestationType .BASIC ;
43+ }
44+
45+ @ Override
46+ public boolean verifyAttestationSignature (AttestationObject attestationObject , ByteArray clientDataJsonHash ) {
47+ final JsonNode ver = attestationObject .getAttestationStatement ().get ("ver" );
48+ final JsonNode response = attestationObject .getAttestationStatement ().get ("response" );
49+
50+ if (ver == null || !ver .isTextual () ) {
51+ throw new IllegalArgumentException ("attStmt.ver must be set as text! " + ver .toString ());
52+ }
53+
54+ if (response == null || !response .isBinary () ) {
55+ throw new IllegalArgumentException ("attStmt.response must be set to a binary value." );
56+ }
57+
58+ String attStmtString ;
59+ try {
60+ attStmtString = new String (response .binaryValue (), Charset .forName ("UTF-8" ));
61+ } catch (IOException ioe ) {
62+ throw ExceptionUtil .wrapAndLog (log , "reponseNode.isBinary() was true but reponseNode.binaryValue() failed" , ioe );
63+ }
64+
65+ if (attStmtString != null && !attStmtString .isEmpty ()) {
66+ final AndroidSafetynetAttestationStatement attStmtObj = parseAndVerify (attStmtString );
67+ if (attStmtObj != null ) {
68+ final byte [] nonce = attStmtObj .getNonce ();
69+ final boolean isCtsProfileMatch = attStmtObj .isCtsProfileMatch ();
70+
71+ if (isCtsProfileMatch ) {
72+ // Verify that the nonce in the response is identical to the SHA-256 hash of
73+ // the concatenation of authenticatorData and clientDataHash.
74+ ByteArray signedData = attestationObject .getAuthenticatorData ().getBytes ().concat (clientDataJsonHash );
75+ ByteArray hashSignedData = crypto .hash (signedData );
76+ ByteArray nonceByteArray = new ByteArray (nonce );
77+
78+ final int compareResult = hashSignedData .compareTo (nonceByteArray );
79+ return (compareResult == 0 );
80+ }
81+ }
82+ }
83+
84+ return false ;
85+ }
86+
87+ /**
88+ * This code is copied from android-play-saftynet attestion sample.
89+ * @param signedAttestationStatment
90+ * @return
91+ */
92+ private AndroidSafetynetAttestationStatement parseAndVerify (String signedAttestationStatment ) {
93+ // Parse JSON Web Signature format.
94+ JsonWebSignature jws ;
95+ try {
96+ jws = JsonWebSignature .parser (JacksonFactory .getDefaultInstance ())
97+ .setPayloadClass (AndroidSafetynetAttestationStatement .class ).parse (signedAttestationStatment );
98+ } catch (IOException e ) {
99+ System .err .println ("Failure: " + signedAttestationStatment + " is not valid JWS " +
100+ "format." );
101+ return null ;
102+ }
103+
104+ // Verify the signature of the JWS and retrieve the signature certificate.
105+ X509Certificate cert ;
106+ try {
107+ cert = jws .verifySignature ();
108+ if (cert == null ) {
109+ System .err .println ("Failure: Signature verification failed." );
110+ return null ;
111+ }
112+ } catch (GeneralSecurityException e ) {
113+ System .err .println (
114+ "Failure: Error during cryptographic verification of the JWS signature." );
115+ return null ;
116+ }
117+
118+ // Verify the hostname of the certificate.
119+ if (!verifyHostname ("attest.android.com" , cert )) {
120+ System .err .println ("Failure: Certificate isn't issued for the hostname attest.android" +
121+ ".com." );
122+ return null ;
123+ }
124+
125+ // Save the cefrtificate
126+ mX5cCert = cert ;
127+
128+ // Extract and use the payload data.
129+ AndroidSafetynetAttestationStatement stmt = (AndroidSafetynetAttestationStatement ) jws .getPayload ();
130+ return stmt ;
131+ }
132+
133+ /**
134+ * Verifies that the certificate matches the specified hostname.
135+ * Uses the {@link DefaultHostnameVerifier} from the Apache HttpClient library
136+ * to confirm that the hostname matches the certificate.
137+ *
138+ * @param hostname
139+ * @param leafCert
140+ * @return
141+ */
142+ private static boolean verifyHostname (String hostname , X509Certificate leafCert ) {
143+ try {
144+ // Check that the hostname matches the certificate. This method throws an exception if
145+ // the cert could not be verified.
146+ HOSTNAME_VERIFIER .verify (hostname , leafCert );
147+ return true ;
148+ } catch (SSLException e ) {
149+ e .printStackTrace ();
150+ }
151+
152+ return false ;
153+ }
154+ }
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