source: libabac/abac_xml.c @ 9e063cb

/* abac_xml.c, specifically for GENI */

/* in xml, rc in general is, 1 is good, 0 or -1 is bad */

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

#include <libxml/tree.h>
#include <libxml/xmlmemory.h>
#include <libxml/parser.h>

#ifndef XMLSEC_NO_XSLT
#include <libxslt/xslt.h>
#include <libxslt/security.h>
#endif /* XMLSEC_NO_XSLT */

#include <xmlsec/xmlsec.h>
#include <xmlsec/xmltree.h>
#include <xmlsec/xmldsig.h>
#include <xmlsec/base64.h>
#include <xmlsec/templates.h>
#include <xmlsec/crypto.h>
#include <xmlsec/list.h>

#include <openssl/sha.h>

/* from Ted's reader */

/* for accessing GENI privilege credentials */
#define GENI_signed_credential "signed-credential"
#define GENI_credential "credential"
#define GENI_type "type"
#define GENI_serial "serial"
#define GENI_owner_gid "owner_gid"
#define GENI_owner_urn "owner_urn"
#define GENI_target_gid "target_gid"
#define GENI_target_urn "target_urn"
#define GENI_uuid "uuid"
#define GENI_expires "expires"
#define GENI_privileges "privileges"
#define GENI_privilege "privilege"
#define GENI_name "name"
#define GENI_can_delegate "can_delegate"

/* for accessing GENI abac credentials. signed-credential, credential, type and
 * expires are present as well.  */
#define GENI_rt0 "rt0"
#define GENI_version "version"

/* maximum credential stringlen */
#define CREDLEN 1024
/* Maximum version len */
#define VERSIONLEN 256

/* Call perror on str and exit */
static void fatal(const char *str) {
    perror(str);
    exit(20);
}

/* Hex dump the contents of buf (length len) to stderr.  For debugging */
static void dump_it(xmlChar *buf, int len) {
    int i;

    for (i=0; i < len; i++ ) 
        fprintf(stderr, "%02x ", buf[i] & 0xff);
    fprintf(stderr, "\n");
}

/* Convert a SHA1 hash to text for printing or use in strings.  keyid is the
 * hash (SHA_DIGEST_LENGTH bytes long) and text is the output string (at least
 * 2 * SHA_DIGEST_LENGTH +1 bytes long).  The caller is responsible for
 * allocating and deallocating each of them. */
static void sha1_to_text(xmlChar *keyid, xmlChar *text) {
    int i = 0;

    for (i=0; i < SHA_DIGEST_LENGTH; i++) 
        snprintf((char *) text+2*i, 3, "%02x", keyid[i] & 0xff);
}

/*
 * Returns the content pointer of the XML_TEXT node that is the child of the
 * node passed in.  Node must point to an XML_ELEMENT node.  the return value
 * is still part of node's XML document, so treat it as read only. */
static xmlChar *get_element_content(xmlNodePtr node) {
    xmlNodePtr text = NULL;

    if ( node->type != XML_ELEMENT_NODE ) return NULL;
    if ( !( text = node->children) ) return NULL;
    if ( text->type != XML_TEXT_NODE ) return NULL;
    return text->content;
}

/*Find the XML element named field that is a at or below node in the XML
 * document and return a copy of the base64 decoded content of its content.
 * For example, find key daya in a signature and return it base64decoded.  buf
 * is allocated and its length is returned in len.  Any values for buf and len
 * are ignored and overwritten. */
static int get_base64_field(xmlNodePtr node, xmlChar *field, 
        xmlChar **buf, int *len) {
    xmlChar *txt = NULL;

    *buf = NULL;

    if ( !(node = xmlSecFindNode(node, field, xmlSecDSigNs)))
        goto fail;

    if ( !(txt = get_element_content(node))) 
            goto fail;
    
    *len = strlen((char *) txt);
    if ( !(*buf = malloc(*len))) 
        goto fail;

    if ( (*len = xmlSecBase64Decode(txt, *buf, *len)) < 0 ) 
        goto fail;

    return 1;
fail:
    if ( *buf) free(*buf);
    *len = 0;
    return 0;
}
/* Construct an ASN.1 header for a field of type h that is len bytes long.
 * Mosttly this creates the proper length encoding under ASN.1's length
 * encoding rules. buf will contain the new header (and the caller is
 * responsible for making sure it is at least 6 bytes long, though fewer are
 * usually used.  The length of the constructed header is returned. This is
 * used in creating a key hash from key data.*/
static int make_asn1_header(char h, size_t len, xmlChar *buf) {
    if ( len > 0x00ffffff) {
        buf[0] = h;
        buf[1] = 0x84;
        buf[2] = (len >> 24) & 0xff;
        buf[3] = (len >> 16) & 0xff;
        buf[4] = (len >> 8) & 0xff;
        buf[5] = (len) & 0xff;
        return 6;
    } else if ( len > 0x0000ffff ) {
        buf[0] = h;
        buf[1] = 0x83;
        buf[2] = (len >> 16) & 0xff;
        buf[3] = (len >> 8) & 0xff;
        buf[4] = (len) & 0xff;
        return 5;
    } else if ( len > 0x000000ff ) {
        buf[0] = h;
        buf[1] = 0x82;
        buf[2] = (len >> 8) & 0xff;
        buf[3] = (len) & 0xff;
        return 4;
    } else if ( len > 0x80 ) {
        buf[0] = h;
        buf[1] = 0x81;
        buf[2] = (len) & 0xff;
        return 3;
    } else {
        buf[0] = h;
        buf[1] = (len) & 0xff;
        return 2;
    }
}

/* Find the RSA key parameters in the KeyInfo section of the XML document
 * pointed to by doc, construct the ASN.1 encoding of that key and SHA1 hash
 * it.    This gives the standard keyid of that key.  keyid will be the binary
 * encoding of that (the bits of the hash)  sha1_to_text will turn it to text.
 * keyid must be at least SHA_DIGEST_LENGTH bytes long, and the caller is
 * responsible for it. This routine returns 1 on success and 0 on failure. */
static int get_keyid_from_keyinfo(xmlDocPtr doc, xmlChar *keyid) {
    xmlNodePtr root = NULL; /* XML document root */
    xmlNodePtr node = NULL; /* Scratch XML node */

    xmlChar b0[20];         /* Header for the sequence */
    xmlChar b1[20];         /* Header for the modulus */
    xmlChar b2[20];         /* Header for the exponent */
    int l0 = 0;             /* Header length for the sequence */
    int l1 = 0;             /* Header length for the modulus */
    int l2 = 0;             /* Header length for the exponent */

    xmlChar *modBuf = NULL; /* Bytes of the modulus */
    xmlChar *expBuf = NULL; /* Bytes of the exponent */
    int modLen = 0;         /* Length of the modulus */
    int expLen = 0;         /* Length of the exponent */

    SHA_CTX sha;            /* SHA1 hash context */

    int rv = 0;             /* return value */

    if ( !SHA1_Init(&sha)) goto fail;

    if ( !doc || !(root = xmlDocGetRootElement(doc)) ) 
        goto fail;

    /* Find the KeyInfo section to be the root of later searches */
    if ( !(node = xmlSecFindNode(root, 
                    xmlSecNodeKeyInfo, xmlSecDSigNs)))
        goto fail;

    /* Get the binary for the modulus and exponent */
    if ( !get_base64_field(node, (xmlChar *) "Modulus", &modBuf, &modLen)) 
        goto fail;
    if ( !get_base64_field(node, (xmlChar *) "Exponent", &expBuf, &expLen)) 
        goto fail;

    /* Construct the headers for modulus and exponent.  Another weird fact
     * about ASN.1 is that all the integers are signed, so if either the
     * modulus or exponent has the high order bit of its first byte set, the
     * ASN.1 encoding has a 0 byte prepended.  This code appends the 0 byte to
     * the header, which results in the same hash. */
    if ( modBuf[0] & 0x80 ) {
        l1 = make_asn1_header(0x02, modLen +1, b1);
        b1[l1++] = '\0';
    } else {
        l1 = make_asn1_header(0x02, modLen, b1);
    }

    if ( expBuf[0] & 0x80 ) {
        l2 = make_asn1_header(0x02, expLen +1, b2);
        b2[l2++] = '\0';
    } else {
        l2 = make_asn1_header(0x02, expLen, b2);
    }

    /* Sequence header: have to do it after we know the lengths of the inner
     * headers. */
    l0 = make_asn1_header(0x30, modLen + expLen + l1 + l2, b0);
    /* Hash it all up in parts */
    SHA1_Update(&sha, b0, l0);
    SHA1_Update(&sha, b1, l1);
    SHA1_Update(&sha, modBuf, modLen);
    SHA1_Update(&sha, b2, l2);
    SHA1_Update(&sha, expBuf, expLen);
    SHA1_Final(keyid, &sha);
    rv = 1;
fail:

    if (modBuf) free(modBuf);
    if (expBuf) free(expBuf);
    return rv;
}

/* Check the signature of either kind of credential - it'll work for basically
 * any signed XML. Returns true if the signature checks and false otherwise.
 * Takes a pointer to the XML document to check.  Similar to the examples at
 * http://www.aleksey.com/xmlsec/api/xmlsec-examples.html */
static int check_signature(xmlDocPtr doc) {
    xmlNodePtr root = NULL;         /* Root XML node */
    xmlNodePtr node = NULL;         /* Scratch XML node */
    xmlSecKeyInfoCtxPtr keyCtx = NULL;/* Key info context.  Used to parse
                                         KeyInfo */
    xmlSecKeysMngrPtr keyMan = NULL;/* Key manager - used because we have
                                       certificated. */
    xmlSecKeyPtr key = NULL;        /* The key extracted */
    xmlSecDSigCtxPtr dsigCtx = NULL;/* Signature context */
    int rv = 0;                     /* Return value */

    if ( doc && !(root = xmlDocGetRootElement(doc)) ) 
        goto fail;

    /* Find the KeyInfo section to pull the keys out. */
    if ( !(node = xmlSecFindNode(root, 
                    xmlSecNodeKeyInfo, xmlSecDSigNs)))
        goto fail;

    /* Create and initialize key, key manager, and context */
    if ( !(key = xmlSecKeyCreate() ) )
            goto fail;
    if ( !(keyMan = xmlSecKeysMngrCreate()) ) 
        goto fail;

    if ( xmlSecCryptoAppDefaultKeysMngrInit(keyMan) < 0)
        goto fail;

    if ( !(keyCtx = xmlSecKeyInfoCtxCreate(keyMan)) ) 
        goto fail;

    /* Do not check certificate signatures */
    keyCtx->flags |= XMLSEC_KEYINFO_FLAGS_X509DATA_DONT_VERIFY_CERTS;

    /* Gather up the key data */
    if ( xmlSecKeyInfoNodeRead(node, key, keyCtx) < 0 ) 
        goto fail;

    /* Set up the signature context and attack the keys */
    if ( !(dsigCtx = xmlSecDSigCtxCreate(NULL)))
        goto fail;

    dsigCtx->signKey = key;

    /* find the Signature section */
    if ( !(node = xmlSecFindNode(root, 
                    xmlSecNodeSignature, xmlSecDSigNs)))
        goto fail;

    /* Check it */
    if ( (rv = xmlSecDSigCtxVerify(dsigCtx, node)) < 0 ) 
        goto fail;

    /* Strangely xmlSecDSigCtxVerify can return success even if the status is
     * bad.  Check the status in the context explicitly and override the result
     * above if necessary.*/
    if ( dsigCtx->status != xmlSecDSigStatusSucceeded) 
        goto fail;

    return 1;
fail:
    if ( key ) xmlSecKeyDestroy(key);
    if ( keyCtx ) xmlSecKeyInfoCtxDestroy(keyCtx);
    if ( dsigCtx) xmlSecDSigCtxDestroy(dsigCtx);
    return 0;
}

/* Parse the content of the expires field and compare it to the time passed in
 * n.  If expires is earlier, return false, else true.  If n is null, compare
 * it to the current time. */
static int check_GENI_expires(xmlChar *expires, struct tm *n) {
    struct tm tv;   /* Parsed expires field */
    time_t now;     /* Now in seconds since the epoch */
    time_t exp;     /* expires in seconds since the epoch */

    if (n) now = mktime(n);
    else time(&now);

    strptime((char *) expires, "%FT%TZ", &tv);
    exp = timegm(&tv);

    return difftime(exp, now) > 0.0;
}

/* Convert a parsed privilege in a GENI privilege string into one or more ABAC
 * creds.  Rules are as in http://groups.geni.net/geni/wiki/TIEDCredentials .
 * keyid is  the issuer's keyid, text_owner is the owners keyid (XXX:a
 * placeholder) text_target is the target's keyid (XXX: a placeholder), priv is
 * the privilege being assigned, and delegate is true if it can be delegated.
 * carray is the output array of character strings that currently has *nc
 * entries in it.  If nc has nothing in it, insert the "speaks_for" delegation
 * rules.  Then add the privilege specific rules. On failure ***carray and its
 * contents are freed and *nc is set to zero.*/
static void add_privilege_credential_string(xmlChar *text_keyid, xmlChar *text_owner, 
        xmlChar *text_target, xmlChar *priv, int delegate, xmlChar ***carray,
        int *nc) {
    xmlChar **rv = *carray;     /* Local pointer to the array of strings */
    xmlChar **newrv = NULL;     /* Used to realloc the array of strings */
    int ncred = *nc;            /* Local copy of the number of creds in rv */
    int newc = (delegate) ? 3 : 1;  /* Number of new creds to add */
    int base = ncred;           /* First new credential index.  This advances
                                   as we add creds to rv. */
    int i = 0;                  /* Scratch */

    /* If rv is empty, add the speaks_for rules */
    if (base == 0 ) newc += 2;

    /* Resize rv */
    if (!(newrv = realloc(rv, (base + newc) * sizeof(xmlChar *))))
        goto fail;
    for ( i = 0; i < base +newc; i ++) 
        newrv[i] = (i < base) ? rv[i] : NULL;

    /* So fail works */
    rv = newrv;
    ncred = base + newc;

    /* Add speaks_for rules  if needed */
    if ( base == 0 ) {
        if ( !(rv[base] = malloc(CREDLEN))) goto fail;
        snprintf((char *) rv[base], CREDLEN, 
                "%s.speaks_for_%s <- %s.speaks_for_%s",
                text_keyid, text_owner, text_owner, text_owner);
        base++;
        if ( !(rv[base] = malloc(CREDLEN))) goto fail;
        snprintf((char *) rv[base], CREDLEN, 
                "%s.speaks_for_%s <- %s",
                text_keyid, text_owner, text_owner);
        base++;
    }

    /* The assignemnt of priv.  Always happens */
    if ( !(rv[base] = malloc(CREDLEN))) goto fail;
    snprintf((char *) rv[base], CREDLEN, 
            "%s.%s_%s <- %s.speaks_for_%s",
            text_keyid, priv, text_target, text_keyid, text_owner);
    base++;
    /* Add delegation rules */
    if ( delegate ) {
        if ( !(rv[base] = malloc(CREDLEN))) goto fail;
        snprintf((char *) rv[base], CREDLEN, 
                "%s.%s_%s <- %s.can_delegate_%s_%s.%s_%s",
                text_keyid, priv, text_target, text_keyid, priv, 
                text_target, priv, text_target);
        base++;
        if ( !(rv[base] = malloc(CREDLEN))) goto fail;
        snprintf((char *) rv[base], CREDLEN, 
                "%s.can_delegate_%s_%s <- %s",
                text_keyid, priv, text_target, text_owner);
        base++;
    }
    /* And return new values */
    *carray = rv;
    *nc = ncred;
    return;
fail:
    if ( rv ) {
        /* Delete all the allocations, ours or not, and clear the caller's 
         * variables */
        for (i = 0; i < ncred; i++) 
            if (rv[i]) free(rv[i]);
        free(rv);
    }
    *carray = NULL;
    *nc = 0;
}

/* Parse a GENI privilege credential (that has already had its signature
 * checked) and return the RT0 strings that the credential is encoded as.  The
 * return value is an array of strings, zero-terminated (like argv) that holds
 * the RT0 strings.  It is NULL on failure. */
static xmlChar **parse_privilege(xmlDocPtr doc) {
    xmlNodePtr root = NULL;     /* XML root node */
    xmlNodePtr node = NULL;     /* XML scratch node */
    xmlNodePtr owner = NULL;    /* XML owner_gid node */
    xmlNodePtr expires = NULL;  /* XML expires node */
    xmlNodePtr target = NULL;   /* XML target_gid node */
    xmlNodePtr privs = NULL;    /* XML privileges node */
    xmlNodePtr priv = NULL;     /* XML privilege node - used to iterate */
    xmlChar keyid[SHA_DIGEST_LENGTH];   /* Issuer key SHA1 */
    xmlChar text_keyid[2*SHA_DIGEST_LENGTH+1];/* Issuer keyid as text */
    xmlChar **newrv = NULL;     /* Used to realloc rv to add the NULL
                                   terminator*/
    xmlChar **rv = NULL;        /* return value */
    int ncred = 0;              /* number of creds in rv, incase we need to
                                   deallocate it */
    int i = 0;                  /* scratch */

    if ( doc && !(root = xmlDocGetRootElement(doc)) ) 
        goto fail;

    /* Get the issuer keyid */
    if ( !get_keyid_from_keyinfo(doc, keyid)) 
        goto fail;
    sha1_to_text(keyid, text_keyid);

    /* Find the various fields of interest */
    if ( !(node = xmlSecFindNode(root, (xmlChar *) GENI_credential, NULL)))
        goto fail;

    /* Make sure this is not expired */
    if ( !(expires = xmlSecFindNode(node, (xmlChar *) GENI_expires, NULL)))
        goto fail;

    if ( !check_GENI_expires(get_element_content(expires), NULL))
        goto fail;

    /* XXX: owner and target will be X.509 pem files from which we need to
     * extract keyids for add_privilege_credential_string.  I didn't replciate
     * that code which lives in libabac. Code to get those keyids needs to be
     * added. */
    if ( !(owner = xmlSecFindNode(node, (xmlChar *) GENI_owner_gid, NULL)))
        goto fail;

    if ( !(target = xmlSecFindNode(node, (xmlChar *) GENI_target_gid, NULL)))
        goto fail;

    if ( !(privs = xmlSecFindNode(node, (xmlChar *) GENI_privileges, NULL)))
        goto fail;

    /* Iterate through the privileges, parsing out names and can_delegate and
     * generating the strings from it. */
    for (priv = privs->children; priv; priv = priv->next) {
        /* reinitialized every time around */
        xmlNodePtr n = NULL;
        xmlChar *name = NULL;
        int delegate = -1;

        /* Privilege node */
        if ( priv->type != XML_ELEMENT_NODE || 
                strcmp((char *) priv->name, (char *) GENI_privilege) ) {
            fprintf(stderr, "Bad node!\n");
            goto fail;
        }
        /* looking for name and can_delegate */
        for (n = priv->children; n; n = n->next) {
            if ( n->type != XML_ELEMENT_NODE ) 
                continue;
            if ( !strcmp((char *) n->name, (char *) GENI_name)) {
                name = get_element_content(n);
                continue;
            }
            if ( !strcmp((char *) n->name, (char *) GENI_can_delegate)) {
                xmlChar *boolean = get_element_content(n);

                if ( !strcmp((char *) boolean, "true") ||
                        !strcmp((char *) boolean, "1") ) {
                    delegate = 1;
                } else if ( !strcmp((char *) boolean, "false") ||
                        !strcmp((char *) boolean, "0") ) {
                    delegate = 0;
                } else {
                    fprintf(stderr, "Unknown delegation value %s", boolean);
                }
            }
        }
        /* Found both name and can_delegate, add the RT0 to rv and ncred */
        if ( name && delegate != -1 ) {
            add_privilege_credential_string(text_keyid, 
                    (xmlChar *) "owner-sha1", (xmlChar *) "target-sha1", name,
                    delegate, &rv, &ncred);
            if ( !rv ) goto fail;
        }
    }

    /* Add the terminating NULL */
    if (!(newrv = realloc(rv, ncred+1)))
        goto fail;

    for ( i = 0; i < ncred+1; i ++) 
        newrv[i] = (i < ncred) ? rv[i] : NULL;

    return rv;

fail:
    /* Throw away all of rv if there's an error */
    if ( rv ) {
        for (i = 0; i < ncred; i++) 
            if (rv[i]) free(rv[i]);
        free(rv);
    }
    return NULL;
}

/* Compare the version string (major.minor) to the major and minor numbers, and
 * return true if the version string is >= the major minor pair. */
static int check_GENI_abac_version(xmlChar *version, int major, int minor) {
    xmlChar lversion[VERSIONLEN];   /* Buffer to parse version in */
    xmlChar *lp = &lversion[0];     /* strsep needs a pointer it can modify */
    char *p = NULL;                 /* Scratch */
    char *ep = NULL;                /* used to check the integer parsing */
    int maj = 0;                    /* Parsed major number */
    int min = 0;                    /* Parsed minor number */

    snprintf((char *) lp, VERSIONLEN, "%s", (char *) version);
    if ( !(p = strsep((char **) &lp, "."))) return 0;
    /* lp points t the major number and p to the minor, now we parse integers*/

    maj = strtol((char *) lp, &ep, 10);
    /* If the major version string was empty or (more likely) there were
     * non-digits in it, throw out the result */
    if ( *lp == '\0' || *ep != '\0' ) 
        return 0;
    min = strtol(p, &ep, 10);
    /* Same test on the minor string */
    if ( *p == '\0' || *ep != '\0' ) 
        return 0;

    if (maj > major || (maj == major && min > minor) ) return 0;
    else return 1;
}
/*
 * Parse an ABAC credential (that has had its signature checked.  Make sure it
 * has not expired and that its version is at least 1.0 (XXX: parameterize
 * that), and return the RT0 it encodes as the only entry in an NULL-terminated
 * array of strings (just like parse_privilege). On failure return NULL. */
xmlChar **parse_abac(xmlDocPtr doc) {
    xmlNodePtr root = NULL;     /* XML root node */
    xmlNodePtr node = NULL;     /* XML credential node */
    xmlNodePtr rt0 = NULL;      /* XML rt0 node */
    xmlNodePtr expires = NULL;  /* XML expires node */
    xmlNodePtr version = NULL;  /* XML version node */
    xmlChar keyid[SHA_DIGEST_LENGTH];/* issuer SHA1 hash */
    xmlChar text_keyid[2*SHA_DIGEST_LENGTH+1];/* Issuer keyid in text */
    xmlChar *txt;               /* rt0 content */
    xmlChar **rv = NULL;        /* return value */
    int ncred = 0;              /* number of creds in rv */
    int i = 0;                  /* Scratch (used only in fail:)  */

    if ( doc && !(root = xmlDocGetRootElement(doc)) ) 
        goto fail;

    /* Get the issuer keyid */
    if ( !get_keyid_from_keyinfo(doc, keyid)) 
        goto fail;
    sha1_to_text(keyid, text_keyid);
    /* get the various nodes of interest */
    if ( !(node = xmlSecFindNode(root, (xmlChar *) GENI_credential, NULL)))
        goto fail;
    if ( !(expires = xmlSecFindNode(node, (xmlChar *) GENI_expires, NULL)))
        goto fail;
    if ( !(rt0 = xmlSecFindNode(node, (xmlChar *) GENI_rt0, NULL)))
        goto fail;
    if ( !(version = xmlSecFindNode(node, (xmlChar *) GENI_version, NULL)))
        goto fail;

    /* Check the version and expiration */
    if ( !check_GENI_abac_version(get_element_content(version), 1, 0)) 
        goto fail;
    if ( !check_GENI_expires(get_element_content(expires), NULL))
        goto fail;

    /* read the RT0 and return it */
    if ( !(txt = get_element_content(rt0)) ) goto fail;

    if ( !(rv = malloc(2 * sizeof(xmlChar *)))) goto fail;
    if (!(rv[0] = malloc(strlen((char *) txt)+1))) goto fail;
    ncred++;

    strcpy((char *) rv[0], (char *) txt);
    rv[1] = NULL;

    return rv;
fail:
    if ( rv ) {
        for (i = 0; i < ncred; i++) 
            if (rv[i]) free(rv[i]);
        free(rv);
    }
    return NULL;
}

/* Check and parse a GENI credential.  Return the new RT0 rules in a
 * NULL-terminated array of strings.  If the signature or parsing fails, return
 * NULL. Demultiplexed to parse_privilege or parse_abac to do the parsing and
 * uses check_signature to confirm the sig. */
static xmlChar **read_credential(char *infile, xmlChar **xml) {
    xmlDocPtr doc = xmlParseFile(infile);   /* Parse the document */
    xmlNodePtr node = NULL;                 /* XML scratch node */
    xmlChar *text = NULL;                   /* Text of the type field */
    xmlChar **rv = NULL;                    /* return value from parse_* */

    if ( !check_signature(doc) ) 
        goto fail;
    /* Parse out the type field */
    if ( !(node = xmlDocGetRootElement(doc)) ) 
        goto fail;
    if ( !(node = xmlSecFindNode(node, (xmlChar *) GENI_credential, NULL)))
        goto fail;
    if ( !(node = xmlSecFindNode(node, (xmlChar *) GENI_type, NULL)))
        goto fail;

    if ( !(text = get_element_content(node)) ) 
        goto fail;

    /* Demux on type */
    if ( !strcmp((char *) text, "privilege")) {
        rv = parse_privilege(doc);
    } else if ( !strcmp((char *) text, "abac")) {
        rv = parse_abac(doc);
    } else { 
        goto fail;
    }
    int len=0;
    xmlDocDumpMemoryEnc(doc, xml, &len, "UTF-8");
    if(len == 0)
       goto fail;

fail:
    xmlFreeDoc(doc);
    return rv;
}


/* from Ted's writer */

/* maximum rt0 stringlen */
#define CREDLEN 1024
/* Maximum version len */
#define VERSIONLEN 256

/* XML template for a new RT0 credential.  Fill in the RT0 to store (XML
 * escaped) and the expiration time (formated using strftime_format and
 * strftime). */
xmlChar *template = (xmlChar *) (
"<signed-credential>\n"
"    <credential xml:id=\"ref0\">\n"
"       <type>abac</type>\n"
"       <version>1.0</version>\n"
"       <expires>%s</expires>\n"
"       <rt0>%s</rt0>\n"
"    </credential>\n"
"    <signatures>\n"
"       <Signature xmlns=\"http://www.w3.org/2000/09/xmldsig#\">\n"
"           <SignedInfo>\n"
"               <CanonicalizationMethod Algorithm=\"http://www.w3.org/2001/10/xml-exc-c14n#\"/>\n"
"               <SignatureMethod Algorithm=\"http://www.w3.org/2000/09/xmldsig#rsa-sha1\"/>\n"
"               <Reference URI=\"#ref0\">\n"
"                   <Transforms>\n"
"                       <Transform Algorithm=\"http://www.w3.org/2000/09/xmldsig#enveloped-signature\"/>\n"
"                   </Transforms>\n"
"                   <DigestMethod Algorithm=\"http://www.w3.org/2000/09/xmldsig#sha1\"/>\n"
"                   <DigestValue/>\n"
"               </Reference>\n"
"           </SignedInfo>\n"
"           <SignatureValue/>\n"
"           <KeyInfo>\n"
"             <KeyValue/>\n"
"               <X509Data>\n"
"                   <X509Certificate/>\n"
"                   <X509SubjectName/>\n"
"                   <X509IssuerSerial/>\n"
"               </X509Data>\n"
"           </KeyInfo>\n"
"       </Signature>\n"
"    </signatures>\n"
"</signed-credential>");

char *strftime_fmt = "%FT%TZ";
#define EXPIRESLEN 20

/* Return a copy of str with > < and & replaced by &gt; &lt; and &amp; for
 * embedding in XML.  Caller is responsible for deallocating the return value
 * using xmlFree().
 */
static xmlChar *minimal_xml_escaping(xmlChar *str) {
    /* A quickie translation table with the character to escape, the output
     * string and the length of the output in it. The table is initialized with
     * the three translations we want. */
    static struct esc {
        xmlChar c;
        xmlChar *esc;
        int l;
    } escapes[] = {
        { (xmlChar) '<', (xmlChar *) "&lt;", 4 }, 
        { (xmlChar) '>', (xmlChar *) "&gt;", 4},
        { (xmlChar) '&', (xmlChar *) "&amp;", 5},
        { (xmlChar) '\0', NULL, 0 },
    };

    xmlChar *rv = NULL;     /* Return value */
    xmlChar *p = NULL;      /* Scratch (walking str) */
    xmlChar *q = NULL;      /* Scratch (walking rv) */
    struct esc *e = NULL;   /* Scratch for walking escapes */
    int len = 0;            /* Length of rv */

    /* Walk str and calculate how long the escaped version is */
    for ( p = str; *p ; p++) {
        int foundit = 0;
        for ( e = escapes; !foundit && e->c ; e++ ) {
            if ( *p == e->c ) {
                len += e->l;
                foundit = 1;
            }
        }
        if ( !foundit ) len++;
    }
    /* Allocate the new string */
    q = rv = (xmlChar *) xmlMalloc(len+1);
    /* copy str to rv, escaping when necessary */
    for ( p = str; *p ; p++) {
        int foundit = 0;
        for ( e = escapes; !foundit && e->c ; e++ ) {
            if ( *p == e->c ) {
                strncpy((char *) q, (char *) e->esc, e->l);
                q += e->l;
                foundit = 1;
            }
        }
        if ( !foundit ) *q++ = *p;
    }
    /* terminate rv */
    *q = '\0';
    return rv;
}

/* Make an new GENI abac credential with the rt0 rule that expires secs from
 * now.  cert is the PEM encoded X.509 of the issuer's certificate as a string.
 * certlen is the length of cert.  Returns the XML. Caller is responsible for
 * freeing it. */
static char *make_credential(xmlChar *rt0, int secs, xmlSecByte *cert, 
        xmlSecSize certlen) {
    xmlDocPtr doc = NULL;       /* parsed XML document */
    xmlNodePtr root = NULL;     /* Root of the document */
    xmlNodePtr signNode = NULL; /* <Signature> element */
    xmlSecDSigCtxPtr dsigCtx = NULL;  /* Signing context */
    xmlChar *rt0_escaped = minimal_xml_escaping(rt0); /* RT0, escaped */
    xmlChar *rv = NULL;         /* return value */
    time_t exp;                 /* expriation time (seconds since epoch) */
    struct tm exp_tm;           /* expiration for formatting */
    char estr[EXPIRESLEN+1];    /* String with formatted expiration */
    char *temp = NULL;          /* populated XML template */
    int len = 0;                /* length of the populated template (temp) */

    if ( !rt0_escaped) goto fail;

    /* Calculate the length of the populated template and allocate it */
    len = strlen((char *) template)+EXPIRESLEN+strlen((char *) rt0_escaped)+1;

    if ( !(temp = malloc(len)) )
        goto fail;

    /* format expiration */
    time(&exp);
    exp += secs;
    gmtime_r(&exp, &exp_tm);

    if (strftime(estr, EXPIRESLEN+1, strftime_fmt, &exp_tm) == 0 ) 
        goto fail;

    /* Populate template with  expiration and escaped rt0 */
    snprintf(temp, len, (char *) template, estr, (char *) rt0_escaped);

    /* parse the populated template */
    if ( !(doc = xmlParseMemory(temp, len))) 
        goto fail;

    if (!(root = xmlDocGetRootElement(doc)) )
        goto fail;

    /* Find the signature element for the Signing call */
    signNode = xmlSecFindNode(root, xmlSecNodeSignature, xmlSecDSigNs);

    /* Create the context */
    if ( !(dsigCtx = xmlSecDSigCtxCreate(NULL))) 
        goto fail;

    /* Assign the key (a PEM key) */
    if (!(dsigCtx->signKey = xmlSecCryptoAppKeyLoadMemory(cert, certlen,
                    xmlSecKeyDataFormatPem, NULL, NULL, NULL)) )
        goto fail;

    /* Load the certificate */
    if ( xmlSecCryptoAppKeyCertLoadMemory(dsigCtx->signKey, cert, certlen,
                xmlSecKeyDataFormatPem) < 0)
        goto fail;

    /* Sign it */
    if ( xmlSecDSigCtxSign(dsigCtx, signNode) < 0)
        goto fail;

    /* Store the signed credential to rv */
    xmlDocDumpMemoryEnc(doc, &rv, &len, "UTF-8");
fail:
    /* clean up */
    if (dsigCtx) 
        xmlSecDSigCtxDestroy(dsigCtx);
    if ( doc) xmlFreeDoc(doc);
    if (rt0_escaped) xmlFree(rt0_escaped);
    if ( temp) free(temp);
    return (char *) rv;
}

#define CERTSIZE 4096
/* Read a file into a the dynamically allocated array buf.  Whatever was in buf
 * is discarded w/o freeing so it should initially be NULL and len 0. On return
 * buf contains as much of the contents of filename as possible and len is the
 * length of it.  The caller must free() buf. buf is zero terminated.*/
static void read_cert(char *filename, char **buf, int *len) {
    FILE *cert = NULL;
    char *nbuf = NULL;
    int cap = CERTSIZE;
    int r = 0;

    *len = 0; 
    if (!(*buf = malloc(CERTSIZE))) return;

    if ( !(cert = fopen(filename, "r"))) 
        goto fail;

    /* Read cert, expanding buf as necessary */
    while ( (r = fread(*buf + *len, 1, cap - *len, cert)) != 0) {
        *len += r;
        if ( *len == cap ) {
            if ( !(nbuf = realloc(*buf, cap + CERTSIZE)) ) 
                goto fail;
            memcpy(nbuf, *buf, cap);
            cap += CERTSIZE;
            *buf = nbuf;
        }
    }
    /* Extend if we read exactly cap bytes so we can terminate the string */
    if ( *len == cap ) {
        if ( !(nbuf = realloc(*buf, cap + CERTSIZE)) ) 
            goto fail;
        memcpy(nbuf, *buf, cap);
        cap += CERTSIZE;
        *buf = nbuf;
    }
    (*buf)[*len] = '\0';
    return;
fail:
    if ( *buf) free(*buf);
    *buf = NULL;
    *len = 0;
    return;
}


/******** helper functions used by libabac **********************/

/* Straight off http://www.aleksey.com/xmlsec/api/xmlsec-examples.html .
 * Voodoo.  But call it. */
int init_xmlsec() {
    /* Init xmlsec library */
    if(xmlSecInit() < 0) {
        fprintf(stderr, "Error: xmlsec initialization failed.\n");
        return(-1);
    }

    /* Check loaded library version */
    if(xmlSecCheckVersion() != 1) {
        fprintf(stderr,
                "Error: loaded xmlsec library version is not compatible.\n");
        return(-1);
    }

    /* Load default crypto engine if we are supporting dynamic
     * loading for xmlsec-crypto libraries. Use the crypto library
     * name ("openssl", "nss", etc.) to load corresponding 
     * xmlsec-crypto library.
     */
#ifdef XMLSEC_CRYPTO_DYNAMIC_LOADING
    if(xmlSecCryptoDLLoadLibrary(BAD_CAST XMLSEC_CRYPTO) < 0) {
        fprintf(stderr, "Error: unable to load default xmlsec-crypto library. "
                "Make sure\n" 
                "that you have it installed and check shared libraries path\n"
                "(LD_LIBRARY_PATH) envornment variable.\n");
        return(-1);     
    }
#endif /* XMLSEC_CRYPTO_DYNAMIC_LOADING */

    /* Init crypto library */
    if(xmlSecCryptoAppInit(NULL) < 0) {
        fprintf(stderr, "Error: crypto initialization failed.\n");
        return(-1);
    }

    /* Init xmlsec-crypto library */
    if(xmlSecCryptoInit() < 0) {
        fprintf(stderr, "Error: xmlsec-crypto initialization failed.\n");
        return(-1);
    }
    return 0;
}

int deinit_xmlsec() {
  /* no op for now */
    return 0;
}


/* to cast the parameters */
char **my_read_credential(char *infile, char **xml) {
    return (char **)read_credential(infile, (xmlChar **)xml);
}

char *my_make_credential(char* rt0, int secs, char* cert, int certlen)
{
    return make_credential((xmlChar *)rt0, secs, (xmlSecByte *)cert, (xmlSecSize)certlen);
}

/* parse the xml blob and extract keyid */ 
char *get_keyid_from_xml(char *xml) {
    xmlDocPtr doc=xmlParseMemory(xml,strlen(xml));
    xmlChar keyid[SHA_DIGEST_LENGTH];   /* Issuer key SHA1 */
    xmlChar text_keyid[2*SHA_DIGEST_LENGTH+1];/* Issuer keyid as text */
    char *ret=NULL;

    /* Get the issuer keyid */
    if ( !get_keyid_from_keyinfo(doc, keyid))
        goto fail;
    sha1_to_text(keyid, text_keyid);
    ret=strdup((char *)text_keyid);
fail:
    xmlFreeDoc(doc);
    return ret;
}

/* parse xml and get the expected expiration time and returns 
 * (expiration time-current time)
 */
long get_validity_from_xml(char *xml) {
    xmlDocPtr doc=xmlParseMemory(xml,strlen(xml));
    xmlNodePtr node = NULL;                 /* XML scratch node */
    xmlNodePtr expires = NULL;  /* XML expires node */
    struct tm tv;   /* Parsed expires field */
    time_t now;     /* Now in seconds since the epoch */
    time_t exp;     /* expires in seconds since the epoch */
    long dtime=0;

    if ( !(node = xmlDocGetRootElement(doc)) )
        goto fail;

    if ( !(expires = xmlSecFindNode(node, (xmlChar *) GENI_expires, NULL)))
        goto fail;

    xmlChar *etime=get_element_content(expires);
    time(&now);

    strptime((char *) etime, "%FT%TZ", &tv);
    exp = timegm(&tv);
    dtime=difftime(exp, now);

fail:
    xmlFreeDoc(doc);
    return dtime;
}

/* parse xml structure and extract the attribute rules */
char **get_rt0_from_xml(char *xml) {
    xmlDocPtr doc=xmlParseMemory(xml,strlen(xml));
    xmlNodePtr node = NULL;                 /* XML scratch node */
    xmlChar *text = NULL;                   /* Text of the type field */
    xmlChar **rv = NULL;                    /* return value from parse_* */
    
    if ( !check_signature(doc) )
        goto fail;
    /* Parse out the type field */
    if ( !(node = xmlDocGetRootElement(doc)) )
        goto fail;
    if ( !(node = xmlSecFindNode(node, (xmlChar *) GENI_credential, NULL)))
        goto fail;
    if ( !(node = xmlSecFindNode(node, (xmlChar *) GENI_type, NULL)))
        goto fail;

    if ( !(text = get_element_content(node)) )
        goto fail;

    /* Demux on type */
    if ( !strcmp((char *) text, "privilege")) {
        rv = parse_privilege(doc);
    } else if ( !strcmp((char *) text, "abac")) {
        rv = parse_abac(doc);
    } else {
        goto fail;
    }
fail:
    xmlFreeDoc(doc);
    return (char **)rv;
}