Implement both direct and advanced lookup URIs

wkd-java/src/main/java/pgp/wkd/WKDAddress.java

@@ -0,0 +1,156 @@
+// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package pgp.wkd;
+
+import java.io.UnsupportedEncodingException;
+import java.net.URI;
+import java.net.URLEncoder;
+import java.nio.charset.Charset;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import org.apache.commons.codec.binary.ZBase32;
+
+/**
+ * Transform an email address into a WKD address.
+ *
+ * @see <a href="https://datatracker.ietf.org/doc/draft-koch-openpgp-webkey-service/">OpenPGP Web Key Directory</a>
+ */
+public final class WKDAddress {
+
+    // RegEx for Email Addresses.
+    // https://www.baeldung.com/java-email-validation-regex#regular-expression-by-rfc-5322-for-email-validation
+    // Modified by adding capture groups '()' for local and domain part
+    private static final Pattern PATTERN_EMAIL = Pattern.compile("^([a-zA-Z0-9_!#$%&'*+/=?`{|}~^.-]+)@([a-zA-Z0-9.-]+)$");
+
+    // Firstname Lastname <email@address> [Optional Comment]
+    // we are only interested in "email@address"
+    private static final Pattern PATTERN_USER_ID = Pattern.compile("^.*\\<([a-zA-Z0-9_!#$%&'*+/=?`{|}~^.-]+@[a-zA-Z0-9.-]+)\\>.*");
+
+    private static final ZBase32 zBase32 = new ZBase32();
+    private static final Charset utf8 = Charset.forName("UTF8");
+
+    private static final String SCHEME = "https://";
+    private static final String SUBDOMAIN = "openpgpkey";
+    private static final String PATH = "/.well-known/openpgpkey/";
+    private static final String HU = "/hu/";
+    private static final String PATH_HU = "/.well-known/openpgpkey/hu/";
+
+    private WKDAddress() {
+
+    }
+
+    public static String emailFromUserId(String userId) {
+        Matcher matcher = PATTERN_USER_ID.matcher(userId);
+        if (!matcher.matches()) {
+            throw new IllegalArgumentException("User-ID does not follow excepted pattern \"Firstname Lastname <email.address> [Optional Comment]\"");
+        }
+
+        String email = matcher.group(1);
+        return email;
+    }
+
+    public static URI directFromUserId(String userId) {
+        String email = emailFromUserId(userId);
+        return directFromEmail(email);
+    }
+
+    public static URI directFromEmail(String email) {
+        MailAddress mailAddress = parseMailAddress(email);
+
+        return URI.create(SCHEME + mailAddress.getDomainPart() + PATH_HU + mailAddress.getHashedLocalPart() + "?l=" + mailAddress.getPercentEncodedLocalPart());
+    }
+
+    /**
+     * Extract the email address from a user-id.
+     * The user-id is expected to correspond to a RFC2822 name-addr.
+     * The email address is expected to be framed by angle brackets.
+     *
+     * @see <a href="https://datatracker.ietf.org/doc/html/rfc2822#section-3.4">RFC2822 - Internet Message Format §3.4: Address Specification</a>
+     * @param userId user-id name-addr
+     * @return WKD URI
+     *
+     * @throws IllegalArgumentException in case the user-id does not match the expected format
+     */
+    public static URI advancedFromUserId(String userId) {
+        String email = emailFromUserId(userId);
+        return advancedFromEmail(email);
+    }
+
+    /**
+     * Translate an email address (localpart@domainpart) to a WKD URI.
+     *
+     * @param email email address
+     * @return WKD URI
+     * @throws IllegalArgumentException in case of a malformed email address
+     */
+    public static URI advancedFromEmail(String email) {
+        MailAddress mailAddress = parseMailAddress(email);
+
+        return URI.create(
+                SCHEME + SUBDOMAIN + "." + mailAddress.getDomainPart() + PATH + mailAddress.getDomainPart()
+                        + HU + mailAddress.getHashedLocalPart() + "?l=" + mailAddress.getPercentEncodedLocalPart()
+        );
+    }
+
+    private static MailAddress parseMailAddress(String email) {
+        Matcher matcher = PATTERN_EMAIL.matcher(email);
+        if (!matcher.matches()) {
+            throw new IllegalArgumentException("Invalid email address.");
+        }
+
+        String localPart = matcher.group(1);
+        String domainPart = matcher.group(2);
+        return new MailAddress(localPart, domainPart);
+    }
+
+    private static class MailAddress {
+        private final String localPart;
+        private final String domainPart;
+
+        MailAddress(String localPart, String domainPart) {
+            this.localPart = localPart;
+            this.domainPart = domainPart;
+        }
+
+        public String getLocalPart() {
+            return localPart;
+        }
+
+        public String getLowerCaseLocalPart() {
+            return getLocalPart().toLowerCase();
+        }
+
+        public String getPercentEncodedLocalPart() {
+            try {
+                return URLEncoder.encode(getLocalPart(), "UTF-8");
+            } catch (UnsupportedEncodingException e) {
+                // UTF8 is a MUST on JVM implementations
+                throw new AssertionError(e);
+            }
+        }
+
+        public String getHashedLocalPart() {
+            MessageDigest sha1;
+            try {
+                sha1 = MessageDigest.getInstance("SHA1");
+            } catch (NoSuchAlgorithmException e) {
+                // SHA-1 is a MUST on JVM implementations
+                throw new AssertionError(e);
+            }
+            sha1.update(getLowerCaseLocalPart().getBytes(utf8));
+            byte[] digest = sha1.digest();
+
+            String base32KeyHandle = zBase32.encodeAsString(digest);
+            return base32KeyHandle;
+        }
+
+        public String getDomainPart() {
+            return domainPart.toLowerCase();
+        }
+    }
+}