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package java.security.cert;

import java.io.IOException;
import java.security.PublicKey;

import javax.security.auth.x500.X500Principal;

import sun.security.x509.NameConstraintsExtension;
import sun.security.x509.X500Name;

/**
 * A trust anchor or most-trusted Certification Authority (CA).
 * <p>
 * This class represents a "most-trusted CA", which is used as a trust anchor
 * for validating X.509 certification paths. A most-trusted CA includes the
 * public key of the CA, the CA's name, and any constraints upon the set of
 * paths which may be validated using this key. These parameters can be
 * specified in the form of a trusted {@code X509Certificate} or as
 * individual parameters.
 * <p>
 * <b>Concurrent Access</b>
 * <p>All {@code TrustAnchor} objects must be immutable and
 * thread-safe. That is, multiple threads may concurrently invoke the
 * methods defined in this class on a single {@code TrustAnchor}
 * object (or more than one) with no ill effects. Requiring
 * {@code TrustAnchor} objects to be immutable and thread-safe
 * allows them to be passed around to various pieces of code without
 * worrying about coordinating access. This stipulation applies to all
 * public fields and methods of this class and any added or overridden
 * by subclasses.
 *
 * @see PKIXParameters#PKIXParameters(Set)
 * @see PKIXBuilderParameters#PKIXBuilderParameters(Set, CertSelector)
 *
 * @since       1.4
 * @author      Sean Mullan
 */
public class TrustAnchor {

    private final PublicKey pubKey;
    private final String caName;
    private final X500Principal caPrincipal;
    private final X509Certificate trustedCert;
    private byte[] ncBytes;
    private NameConstraintsExtension nc;

    /**
     * Creates an instance of {@code TrustAnchor} with the specified
     * {@code X509Certificate} and optional name constraints, which
     * are intended to be used as additional constraints when validating
     * an X.509 certification path.
     * <p>
     * The name constraints are specified as a byte array. This byte array
     * should contain the DER encoded form of the name constraints, as they
     * would appear in the NameConstraints structure defined in
     * <a href="http://www.ietf.org/rfc/rfc3280">RFC 3280</a>
     * and X.509. The ASN.1 definition of this structure appears below.
     *
     * <pre>{@code
     *  NameConstraints ::= SEQUENCE {
     *       permittedSubtrees       [0]     GeneralSubtrees OPTIONAL,
     *       excludedSubtrees        [1]     GeneralSubtrees OPTIONAL }
     *
     *  GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree
     *
     *  GeneralSubtree ::= SEQUENCE {
     *       base                    GeneralName,
     *       minimum         [0]     BaseDistance DEFAULT 0,
     *       maximum         [1]     BaseDistance OPTIONAL }
     *
     *  BaseDistance ::= INTEGER (0..MAX)
     *
     *  GeneralName ::= CHOICE {
     *       otherName                       [0]     OtherName,
     *       rfc822Name                      [1]     IA5String,
     *       dNSName                         [2]     IA5String,
     *       x400Address                     [3]     ORAddress,
     *       directoryName                   [4]     Name,
     *       ediPartyName                    [5]     EDIPartyName,
     *       uniformResourceIdentifier       [6]     IA5String,
     *       iPAddress                       [7]     OCTET STRING,
     *       registeredID                    [8]     OBJECT IDENTIFIER}
     * }</pre>
     * <p>
     * Note that the name constraints byte array supplied is cloned to protect
     * against subsequent modifications.
     *
     * @param trustedCert a trusted {@code X509Certificate}
     * @param nameConstraints a byte array containing the ASN.1 DER encoding of
     * a NameConstraints extension to be used for checking name constraints.
     * Only the value of the extension is included, not the OID or criticality
     * flag. Specify {@code null} to omit the parameter.
     * @throws IllegalArgumentException if the name constraints cannot be
     * decoded
     * @throws NullPointerException if the specified
     * {@code X509Certificate} is {@code null}
     */
    public TrustAnchor(X509Certificate trustedCert, byte[] nameConstraints)
    {
        if (trustedCert == null)
            throw new NullPointerException("the trustedCert parameter must " +
                "be non-null");
        this.trustedCert = trustedCert;
        this.pubKey = null;
        this.caName = null;
        this.caPrincipal = null;
        setNameConstraints(nameConstraints);
    }

    /**
     * Creates an instance of {@code TrustAnchor} where the
     * most-trusted CA is specified as an X500Principal and public key.
     * Name constraints are an optional parameter, and are intended to be used
     * as additional constraints when validating an X.509 certification path.
     * <p>
     * The name constraints are specified as a byte array. This byte array
     * contains the DER encoded form of the name constraints, as they
     * would appear in the NameConstraints structure defined in RFC 3280
     * and X.509. The ASN.1 notation for this structure is supplied in the
     * documentation for
     * {@link #TrustAnchor(X509Certificate, byte[])
     * TrustAnchor(X509Certificate trustedCert, byte[] nameConstraints) }.
     * <p>
     * Note that the name constraints byte array supplied here is cloned to
     * protect against subsequent modifications.
     *
     * @param caPrincipal the name of the most-trusted CA as X500Principal
     * @param pubKey the public key of the most-trusted CA
     * @param nameConstraints a byte array containing the ASN.1 DER encoding of
     * a NameConstraints extension to be used for checking name constraints.
     * Only the value of the extension is included, not the OID or criticality
     * flag. Specify {@code null} to omit the parameter.
     * @throws NullPointerException if the specified {@code caPrincipal} or
     * {@code pubKey} parameter is {@code null}
     * @since 1.5
     */
    public TrustAnchor(X500Principal caPrincipal, PublicKey pubKey,
            byte[] nameConstraints) {
        if ((caPrincipal == null) || (pubKey == null)) {
            throw new NullPointerException();
        }
        this.trustedCert = null;
        this.caPrincipal = caPrincipal;
        this.caName = caPrincipal.getName();
        this.pubKey = pubKey;
        setNameConstraints(nameConstraints);
    }

    /**
     * Creates an instance of {@code TrustAnchor} where the
     * most-trusted CA is specified as a distinguished name and public key.
     * Name constraints are an optional parameter, and are intended to be used
     * as additional constraints when validating an X.509 certification path.
     * <p>
     * The name constraints are specified as a byte array. This byte array
     * contains the DER encoded form of the name constraints, as they
     * would appear in the NameConstraints structure defined in RFC 3280
     * and X.509. The ASN.1 notation for this structure is supplied in the
     * documentation for
     * {@link #TrustAnchor(X509Certificate, byte[])
     * TrustAnchor(X509Certificate trustedCert, byte[] nameConstraints) }.
     * <p>
     * Note that the name constraints byte array supplied here is cloned to
     * protect against subsequent modifications.
     *
     * @param caName the X.500 distinguished name of the most-trusted CA in
     * <a href="http://www.ietf.org/rfc/rfc2253.txt">RFC 2253</a>
     * {@code String} format
     * @param pubKey the public key of the most-trusted CA
     * @param nameConstraints a byte array containing the ASN.1 DER encoding of
     * a NameConstraints extension to be used for checking name constraints.
     * Only the value of the extension is included, not the OID or criticality
     * flag. Specify {@code null} to omit the parameter.
     * @throws IllegalArgumentException if the specified
     * {@code caName} parameter is empty {@code (caName.length() == 0)}
     * or incorrectly formatted or the name constraints cannot be decoded
     * @throws NullPointerException if the specified {@code caName} or
     * {@code pubKey} parameter is {@code null}
     */
    public TrustAnchor(String caName, PublicKey pubKey, byte[] nameConstraints)
    {
        if (pubKey == null)
            throw new NullPointerException("the pubKey parameter must be " +
                "non-null");
        if (caName == null)
            throw new NullPointerException("the caName parameter must be " +
                "non-null");
        if (caName.length() == 0)
            throw new IllegalArgumentException("the caName " +
                "parameter must be a non-empty String");
        // check if caName is formatted correctly
        this.caPrincipal = new X500Principal(caName);
        this.pubKey = pubKey;
        this.caName = caName;
        this.trustedCert = null;
        setNameConstraints(nameConstraints);
    }

    /**
     * Returns the most-trusted CA certificate.
     *
     * @return a trusted {@code X509Certificate} or {@code null}
     * if the trust anchor was not specified as a trusted certificate
     */
    public final X509Certificate getTrustedCert() {
        return this.trustedCert;
    }

    /**
     * Returns the name of the most-trusted CA as an X500Principal.
     *
     * @return the X.500 distinguished name of the most-trusted CA, or
     * {@code null} if the trust anchor was not specified as a trusted
     * public key and name or X500Principal pair
     * @since 1.5
     */
    public final X500Principal getCA() {
        return this.caPrincipal;
    }

    /**
     * Returns the name of the most-trusted CA in RFC 2253 {@code String}
     * format.
     *
     * @return the X.500 distinguished name of the most-trusted CA, or
     * {@code null} if the trust anchor was not specified as a trusted
     * public key and name or X500Principal pair
     */
    public final String getCAName() {
        return this.caName;
    }

    /**
     * Returns the public key of the most-trusted CA.
     *
     * @return the public key of the most-trusted CA, or {@code null}
     * if the trust anchor was not specified as a trusted public key and name
     * or X500Principal pair
     */
    public final PublicKey getCAPublicKey() {
        return this.pubKey;
    }

    /**
     * Decode the name constraints and clone them if not null.
     */
    private void setNameConstraints(byte[] bytes) {
        if (bytes == null) {
            ncBytes = null;
            nc = null;
        } else {
            ncBytes = bytes.clone();
            // validate DER encoding
            try {
                nc = new NameConstraintsExtension(Boolean.FALSE, bytes);
            } catch (IOException ioe) {
                IllegalArgumentException iae =
                    new IllegalArgumentException(ioe.getMessage());
                iae.initCause(ioe);
                throw iae;
            }
        }
    }

    /**
     * Returns the name constraints parameter. The specified name constraints
     * are associated with this trust anchor and are intended to be used
     * as additional constraints when validating an X.509 certification path.
     * <p>
     * The name constraints are returned as a byte array. This byte array
     * contains the DER encoded form of the name constraints, as they
     * would appear in the NameConstraints structure defined in RFC 3280
     * and X.509. The ASN.1 notation for this structure is supplied in the
     * documentation for
     * {@link #TrustAnchor(X509Certificate, byte[])
     * TrustAnchor(X509Certificate trustedCert, byte[] nameConstraints) }.
     * <p>
     * Note that the byte array returned is cloned to protect against
     * subsequent modifications.
     *
     * @return a byte array containing the ASN.1 DER encoding of
     *         a NameConstraints extension used for checking name constraints,
     *         or {@code null} if not set.
     */
    public final byte [] getNameConstraints() {
        return ncBytes == null ? null : ncBytes.clone();
    }

    /**
     * Returns a formatted string describing the {@code TrustAnchor}.
     *
     * @return a formatted string describing the {@code TrustAnchor}
     */
    public String toString() {
        StringBuffer sb = new StringBuffer();
        sb.append("[\n");
        if (pubKey != null) {
            sb.append("  Trusted CA Public Key: " + pubKey.toString() + "\n");
            sb.append("  Trusted CA Issuer Name: "
                + String.valueOf(caName) + "\n");
        } else {
            sb.append("  Trusted CA cert: " + trustedCert.toString() + "\n");
        }
        if (nc != null)
            sb.append("  Name Constraints: " + nc.toString() + "\n");
        return sb.toString();
    }
}
