CryptoPermission getCryptoPermission(String alg) 
{
        // Need to convert to uppercase since the crypto perm
        // lookup is case sensitive.
        alg = alg.toUpperCase(Locale.ENGLISH);
        // If CryptoAllPermission is granted by default, we return that.
        // Otherwise, this will be the permission we return if anything goes
        // wrong.
        CryptoPermission defaultPerm = getDefaultPermission(alg);
        if (defaultPerm == CryptoAllPermission.INSTANCE) {
            return defaultPerm;
        }
        // Determine the codebase of the caller of the JCE API.
        // This is the codebase of the first class which is not in
        // javax.crypto.* packages.
        // NOTE: javax.crypto.* package maybe subject to package
        // insertion, so need to check its classloader as well.
        Class[] context = getClassContext();
        URL callerCodeBase = null;
        int i;
        for (i=0; i< context.length; i++) {
            Class cls = context[i];
            callerCodeBase = JceSecurity.getCodeBase(cls);
            if (callerCodeBase != null) {
                break;
            } else {
                if (cls.getName().startsWith("javax.crypto.")) {
                    // skip jce classes since they aren't the callers
                    continue;
                }
                // use default permission when the caller is system classes
                return defaultPerm;
            }
        }
        if (i == context.length) {
            return defaultPerm;
        }
        CryptoPermissions appPerms;
        synchronized (this.getClass()) {
            if (exemptCache.containsKey(callerCodeBase)) {
                appPerms = (CryptoPermissions)exemptCache.get(callerCodeBase);
            } else {
                appPerms = getAppPermissions(callerCodeBase);
                exemptCache.put(callerCodeBase, appPerms);
            }
        }
        if (appPerms == null) {
            return defaultPerm;
        }
        // If the app was granted the special CryptoAllPermission, return that.
        if (appPerms.implies(allPerm)) {
            return allPerm;
        }
        // Check if the crypto permissions granted to the app contain a
        // crypto permission for the requested algorithm that does not require
        // any exemption mechanism to be enforced.
        // Return that permission, if present.
        PermissionCollection appPc = appPerms.getPermissionCollection(alg);
        if (appPc == null) {
            return defaultPerm;
        }
        Enumeration enum_ = appPc.elements();
        while (enum_.hasMoreElements()) {
            CryptoPermission cp = (CryptoPermission)enum_.nextElement();
            if (cp.getExemptionMechanism() == null) {
                return cp;
            }
        }
        // Check if the jurisdiction file for exempt applications contains
        // any entries for the requested algorithm.
        // If not, return the default permission.
        PermissionCollection exemptPc =
            exemptPolicy.getPermissionCollection(alg);
        if (exemptPc == null) {
            return defaultPerm;
        }
        // In the jurisdiction file for exempt applications, go through the
        // list of CryptoPermission entries for the requested algorithm, and
        // stop at the first entry:
        //  - that is implied by the collection of crypto permissions granted
        //    to the app, and
        //  - whose exemption mechanism is available from one of the
        //    registered CSPs
        enum_ = exemptPc.elements();
        while (enum_.hasMoreElements()) {
            CryptoPermission cp = (CryptoPermission)enum_.nextElement();
            try {
                ExemptionMechanism.getInstance(cp.getExemptionMechanism());
                if (cp.getAlgorithm().equals(
                                      CryptoPermission.ALG_NAME_WILDCARD)) {
                    CryptoPermission newCp;
                    if (cp.getCheckParam()) {
                        newCp = new CryptoPermission(
                                alg, cp.getMaxKeySize(),
                                cp.getAlgorithmParameterSpec(),
                                cp.getExemptionMechanism());
                    } else {
                        newCp = new CryptoPermission(
                                alg, cp.getMaxKeySize(),
                                cp.getExemptionMechanism());
                    }
                    if (appPerms.implies(newCp)) {
                        return newCp;
                    }
                }
                if (appPerms.implies(cp)) {
                    return cp;
                }
            } catch (Exception e) {
                continue;
            }
        }
        return defaultPerm;
}

Returns the maximum allowable crypto strength for the given applet/application, for the given algorithm.

 boolean isCallerTrusted() 
{
        // Get the caller and its codebase.
        Class[] context = getClassContext();
        URL callerCodeBase = null;
        int i;
        for (i=0; i< context.length; i++) {
            callerCodeBase = JceSecurity.getCodeBase(context[i]);
            if (callerCodeBase != null) {
                break;
            }
        }
        // The caller is in the JCE framework.
        if (i == context.length) {
            return true;
        }
        //The caller has been verified.
        if (TrustedCallersCache.contains(context[i])) {
            return true;
        }
        // Check whether the caller is a trusted provider.
        try {
            JceSecurity.verifyProviderJar(callerCodeBase);
        } catch (Exception e2) {
            return false;
        }
        TrustedCallersCache.addElement(context[i]);
        return true;
}