75.1 TLS для SMTP: STARTTLS и неявный TLS (465)

- SmtpServer: STARTTLS (RFC 3207) — SslHandler ставится сразу после того, как ответ 220 ушёл открытым текстом; сессия начинается заново; строки, присланные открытым текстом вместе со STARTTLS, не выполняются, соединение закрывается (CVE-2011-0411); свежий декодер строк без остатков открытого текста - неявный TLS на SMTPS_PORT (RFC 8314); AUTH — только внутри TLS (или SMTP_AUTH_WITHOUT_TLS); Received: ESMTPS/ESMTPSA - SmtpTls: свой сертификат (MAIL_TLS_CERT/KEY) или самоподписанный, создаётся один раз в MAIL_TLS_DIR (в образе /app/data/tls); TLS 1.2/1.3 - тесты: STARTTLS + AUTH, подмешанный открытый текст, JavaMail со starttls.required, порт 465, переиспользование сертификата (38 всего) - проверено вживую: openssl s_client -starttls smtp и порт 465, TLSv1.3 α Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
2026-11-05 19:42:10 +01:00
parent 37f6b3ef3d
commit 17d489e400
7 changed files with 431 additions and 24 deletions
@@ -0,0 +1,110 @@
+package com.mailserver.smtp;
+
+import io.netty.handler.ssl.SslContext;
+import io.netty.handler.ssl.SslContextBuilder;
+import org.bouncycastle.asn1.x500.X500Name;
+import org.bouncycastle.asn1.x509.Extension;
+import org.bouncycastle.asn1.x509.GeneralName;
+import org.bouncycastle.asn1.x509.GeneralNames;
+import org.bouncycastle.cert.jcajce.JcaX509CertificateConverter;
+import org.bouncycastle.cert.jcajce.JcaX509v3CertificateBuilder;
+import org.bouncycastle.operator.jcajce.JcaContentSignerBuilder;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.math.BigInteger;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.attribute.PosixFilePermissions;
+import java.security.KeyPair;
+import java.security.KeyPairGenerator;
+import java.security.SecureRandom;
+import java.security.cert.X509Certificate;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.Base64;
+import java.util.Date;
+
+/**
+ * Certificate for SMTP TLS (STARTTLS and implicit TLS):
+ * <ul>
+ *   <li>{@code cert} and {@code key} given (PEM: certificate chain and PKCS#8 key, e.g. from Let's Encrypt) — used as is;</li>
+ *   <li>otherwise a self-signed certificate for the server hostname, created once in {@code dir} and reused —
+ *       enough for encryption between our own services; other servers deliver over it too (MX delivery does not
+ *       check certificates, RFC 7435 opportunistic TLS).</li>
+ * </ul>
+ */
+public final class SmtpTls {
+
+    private static final Logger log = LoggerFactory.getLogger(SmtpTls.class);
+    static final String CERT_FILE = "smtp-cert.pem";
+    static final String KEY_FILE = "smtp-key.pem";
+
+    private SmtpTls() {
+    }
+
+    public static SslContext serverContext(String certFile, String keyFile, Path dir, String hostname) throws Exception {
+        boolean givenCert = certFile != null && !certFile.isBlank();
+        boolean givenKey = keyFile != null && !keyFile.isBlank();
+        if (givenCert != givenKey) {
+            throw new IllegalStateException("TLS: set both the certificate and the key file, or neither");
+        }
+        Path cert;
+        Path key;
+        if (givenCert) {
+            cert = Path.of(certFile);
+            key = Path.of(keyFile);
+            log.info("SMTP TLS: certificate {}", cert);
+        } else {
+            cert = dir.resolve(CERT_FILE);
+            key = dir.resolve(KEY_FILE);
+            if (!Files.exists(cert) || !Files.exists(key)) {
+                selfSigned(hostname, cert, key);
+                log.warn("SMTP TLS: created a self-signed certificate for {} in {}", hostname, dir);
+            } else {
+                log.info("SMTP TLS: self-signed certificate {}", cert);
+            }
+        }
+        return SslContextBuilder.forServer(cert.toFile(), key.toFile())
+                .protocols("TLSv1.3", "TLSv1.2")
+                .build();
+    }
+
+    static void selfSigned(String hostname, Path certFile, Path keyFile) throws Exception {
+        KeyPairGenerator generator = KeyPairGenerator.getInstance("RSA");
+        generator.initialize(2048, new SecureRandom());
+        KeyPair pair = generator.generateKeyPair();
+        X500Name name = new X500Name("CN=" + hostname);
+        Instant now = Instant.now();
+        JcaX509v3CertificateBuilder builder = new JcaX509v3CertificateBuilder(name,
+                new BigInteger(64, new SecureRandom()), Date.from(now.minus(Duration.ofDays(1))),
+                Date.from(now.plus(Duration.ofDays(3650))), name, pair.getPublic());
+        builder.addExtension(Extension.subjectAlternativeName, false,
+                new GeneralNames(new GeneralName(GeneralName.dNSName, hostname)));
+        X509Certificate certificate = new JcaX509CertificateConverter()
+                .getCertificate(builder.build(new JcaContentSignerBuilder("SHA256withRSA").build(pair.getPrivate())));
+
+        Files.createDirectories(keyFile.toAbsolutePath().getParent());
+        write(keyFile, pem("PRIVATE KEY", pair.getPrivate().getEncoded()), true);
+        write(certFile, pem("CERTIFICATE", certificate.getEncoded()), false);
+    }
+
+    private static String pem(String type, byte[] der) {
+        return "-----BEGIN " + type + "-----\n"
+                + Base64.getMimeEncoder(64, new byte[]{'\n'}).encodeToString(der)
+                + "\n-----END " + type + "-----\n";
+    }
+
+    private static void write(Path file, String text, boolean secret) throws IOException {
+        Files.writeString(file, text, StandardCharsets.US_ASCII);
+        if (secret) {
+            try {
+                Files.setPosixFilePermissions(file, PosixFilePermissions.fromString("rw-------"));
+            } catch (UnsupportedOperationException ignored) {
+                // not a POSIX file system
+            }
+        }
+    }
+}