source: java/net/deterlab/abac/Context.java @ 7f614c1

package net.deterlab.abac;

import edu.uci.ics.jung.graph.*;
import edu.uci.ics.jung.graph.util.*;

import java.io.*;
import java.util.*;
import java.util.regex.*;
import java.util.zip.*;
import java.security.*;
import java.security.cert.*;

import org.bouncycastle.asn1.*;
import org.bouncycastle.asn1.x509.*;
import org.bouncycastle.x509.*;
import org.bouncycastle.openssl.*;
import org.bouncycastle.jce.provider.BouncyCastleProvider;

/**
 * Represents a global graph of credentials in the form of principals and
 * attributes.  Contains the identities and credentials that can be used in a
 * proof.
 * @author <a href="http://abac.deterlab.net">ISI ABAC team</a>
 * @version 1.4
 */
public class Context {
    /** Certificate imported successfully */
    public static final int ABAC_CERT_SUCCESS = 0;
    /** Certificate import failed, invalid certificate */
    public static final int ABAC_CERT_INVALID = -1;
    /** Certificate import failed, signature filed */
    public static final int ABAC_CERT_BAD_SIG = -2;
    /** Certificate import failed, unknown issuer */
    public static final int ABAC_CERT_MISSING_ISSUER = -3;

    /** Internal graph representation */
    protected Graph<Role,Credential> g;
    /** Set of edges in the graph that were added by the logic.  */
    protected Set<Credential> derived_edges;
    /** Internal persistent query object */
    protected Query pq;
    /** True when the graph has been changed since the last set of implied
     * edges were calculated. */
    protected boolean dirty;
    /** Set of identities known to this Context. */
    protected Set<Identity> m_identities;
    /** The CredentialFactory for this Context */
    protected CredentialFactory credentialFactory;

    /** Translation from issuer CN to issuer pubkey identifier */
    protected Map<String, String> nicknames;
    /** Translation from issuer pubkey identifier to issuer CN */
    protected Map<String, String> keys;

    /** True once BouncyCastle has been loaded. */
    static boolean providerLoaded = false;

    /**
     * Load the BouncyCastle provider, necessary for ABAC crypto (shouldn't
     * need to be called directly).  This is called from the Context static
     * constructor and static constructors in other ABAC classes that use
     * BouncyCastle crypto (which loads a Context, which calls it as well) to
     * make sure crypto is available.  
     */
    static void loadBouncyCastle() {
        if ( !providerLoaded ) {
            AccessController.doPrivileged(new PrivilegedAction<Object>() {
                public Object run() {
                    Security.addProvider(new BouncyCastleProvider());
                    return null;
                }
            });
            providerLoaded = true;
        }
    }

    /** Load the BouncyCastle provider. */
    static { loadBouncyCastle(); };

    /**
     * The result of a query on this context.  The credentials form a partial
     * or total proof, and success indicates whether the proof succeeded.
     * @author <a href="http://abac.deterlab.net">ISI ABAC team</a>
     * @version 1.4
     */
    public class QueryResult {
        /** Credentials returned */
        protected Collection<Credential> creds;
        /** True if the proof succeeded. */
        protected boolean success;

        /**
         * Construct a result from components.
         * @param c the collection of credentials in the proof
         * @param s a boolean, true if the query succeeded.
         */
        QueryResult(Collection<Credential> c, boolean s) {
            creds = c;
            success = s;
        }

        /**
         * Empty constructor
         */
        public QueryResult() { 
            creds = new TreeSet<Credential>();
            success = false;
        }

        /**
         * Return the credentials in the proof.
         * @return the collection of credentials
         */
        public Collection<Credential> getCredentials() { return creds; }
        /**
         * Return the success in the proof.
         * @return the boolean, true on success
         */
        public boolean getSuccess() { return success; }
    }


    /**
     * Create an empty Context.
     */
    public Context() {
        /* create the graph */
        g = Graphs.<Role,Credential>synchronizedDirectedGraph(
                new DirectedSparseGraph<Role,Credential>());
        derived_edges = new HashSet<Credential>();
        pq = new Query(g);
        dirty = false;
        m_identities = new TreeSet<Identity>();
        nicknames = new TreeMap<String, String>();
        keys = new TreeMap<String, String>();
        try {
            credentialFactory = new CredentialFactory();
        }
        catch (ABACException ignored) { }
    }

    /**
     * Create a context from another context.
     * @param c the Context to copy
     */
    public Context(Context c) {
        this();
        for (Identity i: c.m_identities) 
            load_id_chunk(i);
        for (Credential cr: c.credentials()) 
            load_attribute_chunk(cr);
        derive_implied_edges();
        try {
            credentialFactory = (CredentialFactory) c.credentialFactory.clone();
        }
        catch (CloneNotSupportedException ignored) { } 
    }

    /**
     * Create a Context from a collection of Credentials.  A jabac extension.
     * @param creds the collection of credentials
     */
    public Context(Collection<Credential> creds) {
        this();
        for (Credential c: creds) {
            Identity i = c.issuer();

            if (i != null ) load_id_chunk(i);
            load_attribute_chunk(c);
        }
    }

    /**
     * Load an Identity from a file.
     * @param fn a String containing the file name.
     * @return one of the static int return codes.
     */
    public int load_id_file(String fn) { return load_id_chunk(new File(fn)); }
    /**
     * Load an Identity from a file.
     * @param fn a File containing the file name.
     * @return one of the static int return codes.
     */
    public int load_id_file(File fn) { return load_id_chunk(fn); }
    /**
     * Load an Identity from an object.  Supported objects are an Identity, a
     * String, a File, or a java.security.cert.X509Certificate.  A string
     * creates an new identity, and the others are derived from the contents of
     * the data or file.
     * @param c an object convertable to an identity as above.
     * @return one of the static int return codes.
     */
    public int load_id_chunk(Object c) {
        try {
            if (c instanceof Identity)
                addIdentity((Identity) c);
            else if (c instanceof String) 
                addIdentity(new Identity((String) c));
            else if (c instanceof File) 
                addIdentity(new Identity((File) c));
            else if (c instanceof X509Certificate) 
                addIdentity(new Identity((X509Certificate) c));
            else 
                return ABAC_CERT_INVALID;
        }
        catch (SignatureException sig) {
            return ABAC_CERT_BAD_SIG;
        }
        catch (Exception e) {
            return ABAC_CERT_INVALID;
        }
        return ABAC_CERT_SUCCESS;
    }

    /**
     * Load an attribute certificate from a file.
     * @param fn a String containing the file name.
     * @return one of the static int return codes.
     */
    public int load_attribute_file(String fn) { 
        return load_attribute_chunk(new File(fn));
    }

    /**
     * Load an attribute certificate from a file.
     * @param fn a File containing the file name.
     * @return one of the static int return codes.
     */
    public int load_attribute_file(File fn) { return load_attribute_chunk(fn); }

    /**
     * Load an Credential from an object.  Supported objects are a Credential, a
     * String, a File, or an org.bouncycastle.x509.X509V2AttributeCertificate.
     * A string creates an new Credential, and the others are derived from the
     * contents of the data or file.
     * @param c an object convertable to a Credential as above.
     * @return one of the static int return codes.
     */
    public int load_attribute_chunk(Object c) {
        try {
            Credential[] creds = null;

            if (c instanceof Credential) {
                add_credential((Credential) c);
                return ABAC_CERT_SUCCESS;
            } else if (c instanceof String) {
                creds = credentialFactory.parseCredential(
                        (String) c, m_identities);
            } else if (c instanceof File) {
                creds = credentialFactory.parseCredential(
                        (File) c, m_identities);
            } else if ( c instanceof X509V2AttributeCertificate)  {
                add_credential(new X509Credential((X509V2AttributeCertificate)c,
                            m_identities));
                return ABAC_CERT_SUCCESS;
            } else return ABAC_CERT_INVALID;

            if ( creds == null ) 
                return ABAC_CERT_INVALID;

            for (Credential cc: creds ) 
                add_credential(cc);
        }
        catch (MissingIssuerException sig) {
            return ABAC_CERT_MISSING_ISSUER ;
        }
        catch (BadSignatureException sig) {
            return ABAC_CERT_BAD_SIG;
        }
        catch (CertInvalidException e) {
            return ABAC_CERT_INVALID;
        }
        catch (ABACException ae) {
            return ABAC_CERT_INVALID;
        }
        return ABAC_CERT_SUCCESS;
    }

    /**
     * Determine if prinicpal possesses role in the current context.  If so,
     * return a proof of that, otherwise return a partial proof of it.
     * @param role a String encoding the role to check for.
     * @param principal a String with the principal ID in it.
     * @return a Context.QueryResult containing the result.
     */
    public QueryResult query(String role, String principal) {
        derive_implied_edges();

        Query q = new Query(g);
        Graph<Role, Credential> rg = q.run(role, principal);

        return new QueryResult(rg.getEdges(), q.successful());
    }

    /**
     * Return a collection of the credentials in the graph.s
     * @return a collection of the credentials in the graph.
     */
    public Collection<Credential> credentials() {
        Collection<Credential> creds = new HashSet<Credential>();

        // only non-derived edges
        for (Credential cred : g.getEdges())
            if (!derived_edges.contains(cred))
                creds.add(cred);

        return creds;
    }

    /**
     * Return all the Identities known in this context.  A jabac extension.
     * @return all the Identities known in this context.
     */
    public Collection<Identity> identities() {
        return m_identities;
    }

    /**
     * Returns true if the given Identity is known in this Context.  A jabac
     * extension.
     * @param i the Identity to look for
     * @return a boolean, true if the Identity is known.
     */
    public boolean knowsIdentity(Identity i) { return m_identities.contains(i);}
    /**
     * Returns true if an Identity with the given string representation is
     * known in this Context.  A jabac extension.
     * @param k the string representing the Identity to look for 
     * @return a boolean, true if the Identity is known.
     */
    public boolean knowsKeyID(String k) {
        boolean known = false;
        for (Identity i: m_identities)
            if (k.equals(i.getKeyID())) return true;
        return false;
    }


    /**
     * Add a credential to the graph.
     * @param cred the Credential to add
     */
    protected void add_credential(Credential cred) {
        Role tail = cred.tail();
        Role head = cred.head();

        // explicitly add the vertices, to avoid a null pointer exception
        if ( !g.containsVertex(head)) 
            g.addVertex(head);
        if ( !g.containsVertex(tail)) 
            g.addVertex(tail);

        if (!g.containsEdge(cred))
            g.addEdge(cred, tail, head);

        // add the prereqs of an intersection to the graph
        if (tail.is_intersection())
            for (Role prereq : tail.prereqs())
                g.addVertex(prereq);

        dirty = true;
    }

    /**
     * Remove a credential from the graph.
     * @param cred the Credential to remove
     */
    protected void remove_credential(Credential cred) {
        if (g.containsEdge(cred))
            g.removeEdge(cred);
        dirty = true;
    }

    /**
     * Add a role w/o an edge
     * @param v the Role to add
     */
    protected void add_vertex(Role v) {
        if (!g.containsVertex(v)) {
            g.addVertex(v);
            dirty = true;
        }
    }

    /**
     * Remove a role and connected edges.
     * @param v the Role to remove
     */
    protected void remove_vertex(Role v) {
        if (g.containsVertex(v)) {
            g.removeVertex(v);
            dirty = true;
        }
    }

    /**
     * Derive the implied edges in the graph, according to RT0 derivation rules.
     * They are added to this graph. See "Distributed Credential Chain Discovery
     * in Trust Management" by Ninghui Li et al. for details. Note that a
     * derived linking edge can imply a new intersection edge and vice versa.
     * Therefore we iteratively derive edges, giving up when an iteration
     * produces 0 new edges.
     */
    protected synchronized void derive_implied_edges() {
        // nothing to do on a clean graph
        if (!dirty)
            return;

        clear_old_edges();

        // iteratively derive links. continue as long as new links are added
        while (derive_links_iter() > 0)
            ;
        dirty = false;
    }

    /**
     * Single iteration of deriving implied edges. Returns the number of new
     * links added.
     * @return the number of new links added.
     */
    protected int derive_links_iter() {
        int count = 0;

        /* for every node in the graph.. */
        for (Role vertex : g.getVertices()) {
            if (vertex.is_intersection()) {
                // for each prereq edge:
                //     find set of principals that have the prereq
                // find the intersection of all sets (i.e., principals 
                //     that satisfy all prereqs)
                // for each principal in intersection:
                //     add derived edge

                Set<Role> principals = null;

                for (Role prereq : vertex.prereqs()) {
                    Set<Role> cur_principals = pq.find_principals(prereq);

                    if (principals == null)
                        principals = cur_principals;
                    else
                        // no, they couldn't just call it "intersection"
                        principals.retainAll(cur_principals);

                    if (principals.size() == 0)
                        break;
                }

                // add em
                for (Role principal : principals)
                    if (add_derived_edge(vertex, principal))
                        ++count;
            }

            else if (vertex.is_linking()) {
                // make the rest of the code a bit clearer
                Role A_r1_r2 = vertex;

                Role A_r1 = new Role(A_r1_r2.A_r1());
                String r2 = A_r1_r2.r2();

                /* locate the node A.r1 */
                if (!g.containsVertex(A_r1)) continue; 

                /* for each B that satisfies A_r1 */
                for (Role principal : pq.find_principals(A_r1)) {
                    Role B_r2 = new Role(principal + "." + r2);
                    if (!g.containsVertex(B_r2)) continue;

                    if (add_derived_edge(A_r1_r2, B_r2))
                        ++count;
                }
            }
        }

        return count;
    }

    /**
     * Add a derived edge in the graph. Returns true only if the edge does not
     * exist.
     * @return a boolean, true if an edge has been added
     */
    protected boolean add_derived_edge(Role head, Role tail) {
        // edge exists: return false
        if (g.findEdge(tail, head) != null)
            return false;

        // add the new edge
        Credential derived_edge = new InternalCredential(head, tail);
        derived_edges.add(derived_edge);
        g.addEdge(derived_edge, tail, head);

        return true;
    }

    /**
     * Clear the derived edges that currently exist in the graph. This is done
     * before the edges are rederived. The derived edges in filtered graphs are
     * also cleared.
     */
    protected void clear_old_edges() { 
        for (Credential i: derived_edges) 
            g.removeEdge(i);
        derived_edges = new HashSet<Credential>();
    }
    /**
     * Put the Identity into the set of ids used to validate certificates.
     * Also put the keyID and name into the translation mappings used by Roles
     * to pretty print.  In the role mapping, if multiple ids use the same
     * common name they are disambiguated.  Only one entry for keyid is
     * allowed.
     * @param id the Identity to add
     */
    protected void addIdentity(Identity id) { 
        if (m_identities.contains(id)) {
            //XXX keep more recent
            return;
        }
        m_identities.add(id);
        if (id.getName() != null && id.getKeyID() != null) {
            if ( !keys.containsKey(id.getKeyID()) ) {
                String name = id.getName();
                int n= 1;

                while (nicknames.containsKey(name)) {
                    name = id.getName() + n++;
                }
                nicknames.put(name, id.getKeyID());
                keys.put(id.getKeyID(), name);
            }
        }
    }
    /**
     * Translate either keys to nicknames or vice versa.  Break the string into
     * space separated tokens and then each of them into period separated
     * strings.  If any of the smallest strings is in the map, replace it with
     * the value.
     * @param is the string to manipulate
     * @param m the Map containing translations
     * @return the string after modification
     */
    protected String replace(String is, Map<String, String> m) {
        String rv = "";
        for (String tok: is.split(" ")) {
            String term = "";
            for (String s: tok.split("\\.")) {
                String next = m.containsKey(s) ? m.get(s) : s;

                if (term.isEmpty()) term = next;
                else term += "." + next;
            }
            if (rv.isEmpty()) rv = term;
            else rv += " " + term;
        }
        return rv;
    }

    /**
     * Expand menmonic names in a Role string, e.g. the CN of the issuer
     * certificate, into the full key ID.  Used internally by Roles to provide
     * transparent use of mnemonics
     * @param s the string to expand
     * @return the String after expansion.
     */
    String expandKeyID(String s) { return replace(s, nicknames); }
    /**
     * Convert key IDs to  menmonic names in a Role string.  The inverse of
     * expandKeyID.
     * @param s the string to expand
     * @return the String after expansion.
     */
    String expandNickname(String s) { return replace(s, keys); }

    /**
     * Read the current ZipEntry's bytes from z.  Tedious because there's no
     * way to reliably tell how big the entry is, so we have to rely on a
     * simple expanding array read of the bytes.
     */
    protected byte[] readCurrentZipEntry(ZipInputStream z) throws IOException {
        final int bsize = 4096;
        byte[] buf = new byte[bsize];
        byte[] rv = new byte[0];
        int r = 0;

        // z.read returns -1 at the end of entry
        while ((r = z.read(buf, 0, bsize)) != -1 ) {
            byte[] b = new byte[rv.length + r];

            System.arraycopy(rv, 0, b, 0, rv.length);
            System.arraycopy(buf, 0, b, rv.length, r);
            rv = b;
        }
        return rv;
    }

    /**
     * Import a zip file.  First import all the identities
     * (pem), then the credentials (der) into the credential graph then any
     * alias files into the two maps.  If keys is not null, any key pairs in
     * PEM files are put in there.  If errors is not null, errors reading files
     * are added indexed by filename.  This is a jabac extension.
     * @param s the InputStream to read
     * @param keys a Collection into which to insert unmatched keys
     * @param errors a Map from entry name to generated exception
     * @throws IOException if the file is unreadable.  Per entry exceptions are
     *                     returned in the errors parameter.
     */
    public void load_zip(InputStream s, Collection<KeyPair> keys, 
            Map<String, Exception> errors) throws IOException {
        Map<String, byte[]> derEntries = new HashMap<String, byte[]>();
        Map<String, Identity> ids = new TreeMap<String, Identity>();
        Map<String, KeyPair> kps = new TreeMap<String, KeyPair>();
        int entries = 0;

        ZipInputStream z = new ZipInputStream(s);

        for (ZipEntry ze = z.getNextEntry(); ze != null; ze = z.getNextEntry()){
            try {
                entries++;
                byte[] buf = readCurrentZipEntry(z);
                PEMReader r = new PEMReader(
                        new InputStreamReader(new ByteArrayInputStream(buf)));
                Object o = readPEM(r);

                if ( o != null ) {
                    if (o instanceof Identity) {
                        Identity i = (Identity) o;
                        String kid = i.getKeyID();

                        if (kps.containsKey(kid) ) {
                            i.setKeyPair(kps.get(kid));
                            kps.remove(kid);
                        }
                        else if (i.getKeyPair() == null ) 
                            ids.put(i.getKeyID(), i);

                        load_id_chunk(i);
                    }
                    else if (o instanceof KeyPair ) {
                        KeyPair kp = (KeyPair) o;
                        String kid = extractKeyID(kp.getPublic());

                        if (ids.containsKey(kid)) {
                            Identity i = ids.get(kid);

                            i.setKeyPair(kp);
                            ids.remove(kid);
                        }
                        else {
                            kps.put(kid, kp);
                        }
                    }
                }
                else {
                    // Not a PEM file
                    derEntries.put(ze.getName(),buf);
                    continue;
                }
            }
            catch (Exception e ) {
                if (errors != null ) errors.put(ze.getName(), e);
            }
        }

        for ( String k: derEntries.keySet() ) {
            try {
                Credential[] creds = credentialFactory.parseCredential(
                            new ByteArrayInputStream(derEntries.get(k)),
                            m_identities);
                for (Credential c: creds) 
                    add_credential(c);
            }
            catch (Exception e ) {
                if (errors != null ) errors.put(k, e);
            }
        }

        if (entries == 0) 
            throw new IOException("Not a ZIP file (or empty ZIP file)");
    }
    /**
     * Equivalent to load_zip(s, null, null).
     * @param s the InputStream to read
     * @throws IOException if the file is unreadable. To see per-entry
     *                      exceptions use a signature with the errors parameter
     */
    public void load_zip(InputStream s) 
            throws IOException {
        load_zip(s, null, null);
    }
    /**
     * Equivalent to load_zip(s, null, errors).
     * @param s the InputStream to read
     * @param errors a Map from entry name to generated exception
     * @throws IOException if the file is unreadable.  Per entry exceptions are
     *                     returned in the errors parameter.
     */
    public void load_zip(InputStream s, 
            Map<String, Exception> errors) throws IOException {
        load_zip(s, null, errors);
    }
    /**
     * Equivalent to load_zip(s, keys, null).
     * @param s the InputStream to read
     * @param keys a Collection into which to insert unmatched keys
     * @throws IOException if the file is unreadable. To see per-entry
     *                      exceptions use a signature with the errors parameter
     */
    public void load_zip(InputStream s, 
            Collection<KeyPair> keys) throws IOException {
        load_zip(s, keys, null);
    }

    /**
     * Loads a zip file.  Equivalent to 
     * load_zip(new FileInputStream(zf), keys, errors).
     * @param zf the File to read
     * @param keys a Collection into which to insert unmatched keys
     * @param errors a Map from entry name to generated exception
     * @throws IOException if the file is unreadable.  Per entry exceptions are
     *                     returned in the errors parameter.
     */
    public void load_zip(File zf, Collection<KeyPair> keys, 
            Map<String, Exception> errors) throws IOException {
        load_zip(new FileInputStream(zf), keys, errors);
    }
    /**
     * Equivalent to load_zip(d, null, null).
     * @param d the File to read
     * @throws IOException if the file is unreadable. To see per-entry
     *                      exceptions use a signature with the errors parameter
     */
    public void load_zip(File d) 
            throws IOException {
        load_zip(d, null, null);
    }
    /**
     * Equivalent to load_zip(d, null, errors).
     * @param d the File to read
     * @param errors a Map from entry name to generated exception
     * @throws IOException if the file is unreadable.  Per entry exceptions are
     *                     returned in the errors parameter.
     */
    public void load_zip(File d, 
            Map<String, Exception> errors) throws IOException {
        load_zip(d, null, errors);
    }
    /**
     * Equivalent to load_zip(d, keys, null).
     * @param d the File to read
     * @param keys a Collection into which to insert unmatched keys
     * @throws IOException if the file is unreadable. To see per-entry
     *                      exceptions use a signature with the errors parameter
     */
    public void load_zip(File d, 
            Collection<KeyPair> keys) throws IOException {
        load_zip(d, keys, null);
    }

    /**
     * Read a PEM file that contains an X509 Certificate, a key pair, or both.
     * If a cert is present it is converted into an Identity.  A key pair is
     * returned as a java.security.KeyPair and both are returned as an Identity
     * with an associated key pair.
     * @param r a PEMReader from which to read
     * @return an object encoding the contents (as above)
     * @throws IOException for an unreadable or badly formated input
     */
    protected Object readPEM(PEMReader r) throws IOException {
        Identity i = null;
        KeyPair keys = null;
        Object o = null;

        while ( (o = r.readObject()) != null ) {
            if (o instanceof X509Certificate) {
                if ( i == null ) {
                    try {
                        i = new Identity((X509Certificate)o);
                    }
                    catch (Exception e) {
                        // Translate Idenitiy exceptions to IOException
                        throw new IOException(e);
                    }
                    if (keys != null ) {
                        i.setKeyPair(keys);
                        keys = null;
                    }
                }
                else throw new IOException("Two certificates");
            }
            else if (o instanceof KeyPair ) {
                if ( i != null ) i.setKeyPair((KeyPair) o);
                else keys = (KeyPair) o;
            }
            else {
                throw new IOException("Unexpected PEM object: " + 
                        o.getClass().getName());
            }
        }

        if ( i != null ) return i;
        else if ( keys != null) return keys;
        else return null;
    }

    /**
     * Import a directory full of files.  First import all the identities
     * (pem), then the credentials (der) into the credential graph then any
     * alias files into the two maps.  If keys is not null, any key pairs in
     * PEM files are put in there.  If errors is not null, errors reading files
     * are added indexed by filename.  This behaves slightly differently from
     * the load_directory description in the general libabac documentation.
     * @param d the File to read.  If it is a directory its contents are read
     * @param keys a Collection into which to insert unmatched keys
     * @param errors a Map from entry name to generated exception
     * @throws IOException if the file is unreadable.  Per file exceptions are
     *                     returned in the errors parameter.
     */
    public void load_directory(File d, Collection<KeyPair> keys, 
            Map<String, Exception> errors) {
        Vector<File> derFiles = new Vector<File>();
        Collection<File> files = new Vector<File>();
        Map<String, Identity> ids = new TreeMap<String, Identity>();
        Map<String, KeyPair> kps = new TreeMap<String, KeyPair>();

        if (d.isDirectory() ) 
            for (File f : d.listFiles()) 
                files.add(f);
        else files.add(d);

        for (File f: files ) {
            try {
                PEMReader r = new PEMReader(new FileReader(f));
                Object o = readPEM(r);

                if ( o != null ) {
                    if (o instanceof Identity) {
                        Identity i = (Identity) o;
                        String kid = i.getKeyID();

                        if (kps.containsKey(kid) ) {
                            i.setKeyPair(kps.get(kid));
                            kps.remove(kid);
                        }
                        else if (i.getKeyPair() == null ) 
                            ids.put(i.getKeyID(), i);

                        load_id_chunk(i);
                    }
                    else if (o instanceof KeyPair ) {
                        KeyPair kp = (KeyPair) o;
                        String kid = extractKeyID(kp.getPublic());

                        if (ids.containsKey(kid)) {
                            Identity i = ids.get(kid);

                            i.setKeyPair(kp);
                            ids.remove(kid);
                        }
                        else {
                            kps.put(kid, kp);
                        }
                    }
                }
                else {
                    // Not a PEM file
                    derFiles.add(f);
                    continue;
                }
            }
            catch (Exception e ) {
                if (errors != null ) errors.put(f.getName(), e);
            }
        }

        for ( File f : derFiles ) {
            try {
                Credential[] creds = credentialFactory.parseCredential(f, 
                        m_identities);
                for (Credential c: creds) 
                    add_credential(c);
            }
            catch (Exception e ) {
                if (errors != null ) errors.put(f.getName(), e);
            }
        }
    }
    /**
     * Equivalent to load_directory(d, null, null).
     * @param d the File to read.  If it is a directory its contents are read
     * @throws IOException if the file is unreadable.  To see per-file 
     *                     exceptions use a signature with the errors parameter.
     */
    public void load_directory(File d) {
        load_directory(d, null, null);
    }
    /**
     * Equivalent to load_directory(d, null, null).
     * @param d the File to read.  If it is a directory its contents are read
     * @param errors a Map from entry name to generated exception
     * @throws IOException if the file is unreadable.  Per file exceptions are
     *                     returned in the errors parameter.
     */
    public void load_directory(File d, Map<String, Exception> errors) {
        load_directory(d, null, errors);
    }
    /**
     * Equivalent to load_directory(d, null, null).
     * @param d the File to read.  If it is a directory its contents are read
     * @param keys a Collection into which to insert unmatched keys
     * @throws IOException if the file is unreadable.  To see per-file 
     *                     exceptions use a signature with the errors parameter.
     */
    public void load_directory(File d, Collection<KeyPair> keys) {
        load_directory(d, keys, null);
    }

    /**
     * Load from a simple rt0 text format.  A jabac extension.  The format is
     * <br/>
     * # comments<br/>
     * role &lt;- role<br/>
     * <br/>
     *
     * Spaces are not significant around the arrow and the tail can be as long
     * as needed.
     * @param s the InputStream to load
     * @throws IOException if there is an error getting the file open or in
     * format
     */
    public void load_rt0(InputStream s) 
            throws IOException {
        Pattern comment = Pattern.compile("(^\\s*#|^\\s*$)");
        Pattern rule = Pattern.compile("([\\w\\.]+)\\s*<-+\\s*(.+)");
        LineNumberReader r = new LineNumberReader(new InputStreamReader(s));
        String line = null;

        while ((line = r.readLine()) != null) {
            Matcher cm = comment.matcher(line);
            Matcher rm = rule.matcher(line);

            if (cm.find()) continue;
            if (rm.find()) 
                add_credential(new InternalCredential(new Role(rm.group(1)), 
                            new Role(rm.group(2))));
            else 
                throw new RuntimeException("Unexpected format: line " + 
                        r.getLineNumber());
        }
    }
    /**
     * Equivalent to load_rt0(new FileInputStream(f)
     * @param f the File to load
     * @throws IOException if there is an error getting the file open
     */
    public void load_rt0(File f) throws IOException {
        load_rt0(new FileInputStream(f));
    }
        

    /**
     * Write the certificates that make up the context as a zip file, with an
     * entry for each credential or identity.  The files are all zipped in a
     * directory derived from the filename.
     * @param s the OutputStream to write
     * @param allIDs a boolean, if true write certificates for all Identities,
     * whether used in signing a credential or not.
     * @param withPrivateKeys a boolean, if true write the Identities as PEM
     * file containing both the certificate and the private keys.
     * @throws IOException if there is a problem writing the file.
     */
    public void write_zip(OutputStream s, boolean allIDs, 
            boolean withPrivateKeys) throws IOException {
        ZipOutputStream z = new ZipOutputStream(s);
        Set<Identity> ids = allIDs ?  m_identities : new TreeSet<Identity>();
        String baseDir = "creds";
        int idx = baseDir.indexOf('.');


        if (idx != -1) 
            baseDir = baseDir.substring(0, idx);

        int n = 0;
        for (Credential c: credentials()) {
            z.putNextEntry(new ZipEntry(baseDir + File.separator + 
                        "attr" + n++  + ".der"));
            c.write(z);
            z.closeEntry();
            if ( c.issuer() != null && !allIDs) ids.add(c.issuer());
        }
        for (Identity i: ids) {
            z.putNextEntry(new ZipEntry(baseDir + File.separator + 
                        i.getName() + ".pem"));
            i.write(z);
            if (withPrivateKeys)
                i.writePrivateKey(z);
            z.closeEntry();
        }
        z.close();
    }
    /**
     * Equivalent to
     * write_zip(new FileOutputStream(f), allIDs, withPrivateKeys).
     * @param f the File to write
     * @param allIDs a boolean, if true write certificates for all Identities,
     * whether used in signing a credential or not.
     * @param withPrivateKeys a boolean, if true write the Identities as PEM
     * file containing both the certificate and the private keys.
     * @throws IOException if there is a problem writing the file.
     */
    public void write_zip(File f, boolean allIDs, boolean withPrivateKeys) 
            throws IOException {
        write_zip(new FileOutputStream(f), allIDs, withPrivateKeys);
    }

    /**
     * Write to a simple rt0 text format.  A jabac extension.
     * The format is
     * <br/>
     * role &lt;- role<br/>
     * <br/>
     *
     * @param w a Writer to print on
     * @param useKeyIDs a boolean, true to print key IDs not mnemonics
     */
    public void write_rt0(Writer w, boolean useKeyIDs) {
        PrintWriter pw = w instanceof PrintWriter ? 
            (PrintWriter) w : new PrintWriter(w);

        for (Credential c: credentials()) 
            pw.println(useKeyIDs ? c.toString() : c.simpleString(this));
        pw.flush();
    }

    /**
     * Call write_rt0 on a FileWriter derived from f.
     * @param f the File to write to
     * @param useKeyIDs a boolean, true to print key IDs not mnemonics
     * @throws IOException if there is a problem writing the file.
     */
    public void write_rt0(File f, boolean useKeyIDs) throws IOException {
        write_rt0(new FileWriter(f), useKeyIDs);
    }

    /**
     * Equivalent to write_rt0(w, false);
     * @param w a Writer to print on
     */
    public void write_rt0(Writer w) { write_rt0(w, false); }

    /**
     * Equivalent to write_rt0(f, false);
     * @param f the File to write to
     * @throws IOException if there is a problem writing the file.
     */
    public void write_rt0(File f) throws IOException {
        write_rt0(new FileWriter(f), false);
    }

    /**
     * Return this Context's CredentialFactory.
     * @return this Context's CredentialFactory.
     */
    public CredentialFactory getCredentialFactory() {
        return credentialFactory;
    }

    /**
     * Set this Context's CredentialFactory.
     * @param cf the new CredentialFactoty
     */
    public void setCredentialFactory(CredentialFactory cf) { 
        credentialFactory = cf;
    }

    /**
     * Return a new credential supported by this Context.  It is not inserted
     * in the Context.
     * @param head a Role, the head of the encoded ABAC statement
     * @param tail a Role, the tail of the decoded ABAC statement
     * @return a Credential encoding that ABAC statement
     */
    public Credential newCredential(Role head, Role tail) {
        return credentialFactory.generateCredential(head, tail);
    }

    /**
     * Get to the SHA1 hash of the key.  Used by Roles and Identities to get a
     * key ID.
     * @param k the PublicKey to get the ID from.
     * @return a String with the key identifier
     */
    static String extractKeyID(PublicKey k) {
        SubjectPublicKeyInfo ki = extractSubjectPublicKeyInfo(k);
        SubjectKeyIdentifier id = 
            SubjectKeyIdentifier.createSHA1KeyIdentifier(ki);

        // Now format it into a string for keeps
        Formatter fmt = new Formatter(new StringWriter());
        for (byte b: id.getKeyIdentifier())
            fmt.format("%02x", b);
        return fmt.out().toString();
    }

    /**
     * Extratct the SubjectPublicKeyInfo.  Useful for some other encryptions,
     * notably Certificate.make_cert().
     * @param k the PublicKey to get the ID from.
     * @return a String with the key identifier
     */
    static SubjectPublicKeyInfo extractSubjectPublicKeyInfo(
            PublicKey k) {
        ASN1Sequence seq = null;
        try {
            seq = (ASN1Sequence) new ASN1InputStream(
                    k.getEncoded()).readObject();
        }
        catch (IOException ie) {
            // Badly formatted key??
            return null;
        }
        return new SubjectPublicKeyInfo(seq);
    }

}