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authorDavid Howells <dhowells@redhat.com>2014-07-01 19:40:19 +0400
committerDavid Howells <dhowells@redhat.com>2014-07-08 16:49:56 +0400
commit2e3fadbf730fd0d13c891d5e555af3e7f39ca3f4 (patch)
tree8618dea8bfd135a9e81650adc3080883410fd30e /crypto/asymmetric_keys
parentace0107a3936774e9da2c30cbdc99ad13c103c10 (diff)
downloadlinux-2e3fadbf730fd0d13c891d5e555af3e7f39ca3f4.tar.xz
PKCS#7: Implement a parser [RFC 2315]
Implement a parser for a PKCS#7 signed-data message as described in part of RFC 2315. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Vivek Goyal <vgoyal@redhat.com> Reviewed-by: Kees Cook <keescook@chromium.org>
Diffstat (limited to 'crypto/asymmetric_keys')
-rw-r--r--crypto/asymmetric_keys/Kconfig9
-rw-r--r--crypto/asymmetric_keys/Makefile13
-rw-r--r--crypto/asymmetric_keys/pkcs7.asn1127
-rw-r--r--crypto/asymmetric_keys/pkcs7_parser.c396
-rw-r--r--crypto/asymmetric_keys/pkcs7_parser.h61
5 files changed, 606 insertions, 0 deletions
diff --git a/crypto/asymmetric_keys/Kconfig b/crypto/asymmetric_keys/Kconfig
index 03a6eb95ab50..a7cec9dd6154 100644
--- a/crypto/asymmetric_keys/Kconfig
+++ b/crypto/asymmetric_keys/Kconfig
@@ -37,4 +37,13 @@ config X509_CERTIFICATE_PARSER
data and provides the ability to instantiate a crypto key from a
public key packet found inside the certificate.
+config PKCS7_MESSAGE_PARSER
+ tristate "PKCS#7 message parser"
+ depends on X509_CERTIFICATE_PARSER
+ select ASN1
+ select OID_REGISTRY
+ help
+ This option provides support for parsing PKCS#7 format messages for
+ signature data and provides the ability to verify the signature.
+
endif # ASYMMETRIC_KEY_TYPE
diff --git a/crypto/asymmetric_keys/Makefile b/crypto/asymmetric_keys/Makefile
index 0727204aab68..59d8cade5cfe 100644
--- a/crypto/asymmetric_keys/Makefile
+++ b/crypto/asymmetric_keys/Makefile
@@ -25,3 +25,16 @@ $(obj)/x509_rsakey-asn1.o: $(obj)/x509_rsakey-asn1.c $(obj)/x509_rsakey-asn1.h
clean-files += x509-asn1.c x509-asn1.h
clean-files += x509_rsakey-asn1.c x509_rsakey-asn1.h
+
+#
+# PKCS#7 message handling
+#
+obj-$(CONFIG_PKCS7_MESSAGE_PARSER) += pkcs7_message.o
+pkcs7_message-y := \
+ pkcs7-asn1.o \
+ pkcs7_parser.o
+
+$(obj)/pkcs7_parser.o: $(obj)/pkcs7-asn1.h
+$(obj)/pkcs7-asn1.o: $(obj)/pkcs7-asn1.c $(obj)/pkcs7-asn1.h
+
+clean-files += pkcs7-asn1.c pkcs7-asn1.h
diff --git a/crypto/asymmetric_keys/pkcs7.asn1 b/crypto/asymmetric_keys/pkcs7.asn1
new file mode 100644
index 000000000000..a5a14ef28c86
--- /dev/null
+++ b/crypto/asymmetric_keys/pkcs7.asn1
@@ -0,0 +1,127 @@
+PKCS7ContentInfo ::= SEQUENCE {
+ contentType ContentType,
+ content [0] EXPLICIT SignedData OPTIONAL
+}
+
+ContentType ::= OBJECT IDENTIFIER ({ pkcs7_note_OID })
+
+SignedData ::= SEQUENCE {
+ version INTEGER,
+ digestAlgorithms DigestAlgorithmIdentifiers,
+ contentInfo ContentInfo,
+ certificates CHOICE {
+ certSet [0] IMPLICIT ExtendedCertificatesAndCertificates,
+ certSequence [2] IMPLICIT Certificates
+ } OPTIONAL ({ pkcs7_note_certificate_list }),
+ crls CHOICE {
+ crlSet [1] IMPLICIT CertificateRevocationLists,
+ crlSequence [3] IMPLICIT CRLSequence
+ } OPTIONAL,
+ signerInfos SignerInfos
+}
+
+ContentInfo ::= SEQUENCE {
+ contentType ContentType,
+ content [0] EXPLICIT Data OPTIONAL
+}
+
+Data ::= ANY ({ pkcs7_note_data })
+
+DigestAlgorithmIdentifiers ::= CHOICE {
+ daSet SET OF DigestAlgorithmIdentifier,
+ daSequence SEQUENCE OF DigestAlgorithmIdentifier
+}
+
+DigestAlgorithmIdentifier ::= SEQUENCE {
+ algorithm OBJECT IDENTIFIER ({ pkcs7_note_OID }),
+ parameters ANY OPTIONAL
+}
+
+--
+-- Certificates and certificate lists
+--
+ExtendedCertificatesAndCertificates ::= SET OF ExtendedCertificateOrCertificate
+
+ExtendedCertificateOrCertificate ::= CHOICE {
+ certificate Certificate, -- X.509
+ extendedCertificate [0] IMPLICIT ExtendedCertificate -- PKCS#6
+}
+
+ExtendedCertificate ::= Certificate -- cheating
+
+Certificates ::= SEQUENCE OF Certificate
+
+CertificateRevocationLists ::= SET OF CertificateList
+
+CertificateList ::= SEQUENCE OF Certificate -- This may be defined incorrectly
+
+CRLSequence ::= SEQUENCE OF CertificateList
+
+Certificate ::= ANY ({ pkcs7_extract_cert }) -- X.509
+
+--
+-- Signer information
+--
+SignerInfos ::= CHOICE {
+ siSet SET OF SignerInfo,
+ siSequence SEQUENCE OF SignerInfo
+}
+
+SignerInfo ::= SEQUENCE {
+ version INTEGER,
+ issuerAndSerialNumber IssuerAndSerialNumber,
+ digestAlgorithm DigestAlgorithmIdentifier ({ pkcs7_sig_note_digest_algo }),
+ authenticatedAttributes CHOICE {
+ aaSet [0] IMPLICIT SetOfAuthenticatedAttribute
+ ({ pkcs7_sig_note_set_of_authattrs }),
+ aaSequence [2] EXPLICIT SEQUENCE OF AuthenticatedAttribute
+ -- Explicit because easier to compute digest on
+ -- sequence of attributes and then reuse encoded
+ -- sequence in aaSequence.
+ } OPTIONAL,
+ digestEncryptionAlgorithm
+ DigestEncryptionAlgorithmIdentifier ({ pkcs7_sig_note_pkey_algo }),
+ encryptedDigest EncryptedDigest,
+ unauthenticatedAttributes CHOICE {
+ uaSet [1] IMPLICIT SET OF UnauthenticatedAttribute,
+ uaSequence [3] IMPLICIT SEQUENCE OF UnauthenticatedAttribute
+ } OPTIONAL
+} ({ pkcs7_note_signed_info })
+
+IssuerAndSerialNumber ::= SEQUENCE {
+ issuer Name ({ pkcs7_sig_note_issuer }),
+ serialNumber CertificateSerialNumber ({ pkcs7_sig_note_serial })
+}
+
+CertificateSerialNumber ::= INTEGER
+
+SetOfAuthenticatedAttribute ::= SET OF AuthenticatedAttribute
+
+AuthenticatedAttribute ::= SEQUENCE {
+ type OBJECT IDENTIFIER ({ pkcs7_note_OID }),
+ values SET OF ANY ({ pkcs7_sig_note_authenticated_attr })
+}
+
+UnauthenticatedAttribute ::= SEQUENCE {
+ type OBJECT IDENTIFIER ({ pkcs7_note_OID }),
+ values SET OF ANY
+}
+
+DigestEncryptionAlgorithmIdentifier ::= SEQUENCE {
+ algorithm OBJECT IDENTIFIER ({ pkcs7_note_OID }),
+ parameters ANY OPTIONAL
+}
+
+EncryptedDigest ::= OCTET STRING ({ pkcs7_sig_note_signature })
+
+---
+--- X.500 Name
+---
+Name ::= SEQUENCE OF RelativeDistinguishedName
+
+RelativeDistinguishedName ::= SET OF AttributeValueAssertion
+
+AttributeValueAssertion ::= SEQUENCE {
+ attributeType OBJECT IDENTIFIER ({ pkcs7_note_OID }),
+ attributeValue ANY
+}
diff --git a/crypto/asymmetric_keys/pkcs7_parser.c b/crypto/asymmetric_keys/pkcs7_parser.c
new file mode 100644
index 000000000000..42e56aa7d277
--- /dev/null
+++ b/crypto/asymmetric_keys/pkcs7_parser.c
@@ -0,0 +1,396 @@
+/* PKCS#7 parser
+ *
+ * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#define pr_fmt(fmt) "PKCS7: "fmt
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <linux/slab.h>
+#include <linux/err.h>
+#include <linux/oid_registry.h>
+#include "public_key.h"
+#include "pkcs7_parser.h"
+#include "pkcs7-asn1.h"
+
+struct pkcs7_parse_context {
+ struct pkcs7_message *msg; /* Message being constructed */
+ struct pkcs7_signed_info *sinfo; /* SignedInfo being constructed */
+ struct pkcs7_signed_info **ppsinfo;
+ struct x509_certificate *certs; /* Certificate cache */
+ struct x509_certificate **ppcerts;
+ unsigned long data; /* Start of data */
+ enum OID last_oid; /* Last OID encountered */
+ unsigned x509_index;
+ unsigned sinfo_index;
+};
+
+/**
+ * pkcs7_free_message - Free a PKCS#7 message
+ * @pkcs7: The PKCS#7 message to free
+ */
+void pkcs7_free_message(struct pkcs7_message *pkcs7)
+{
+ struct x509_certificate *cert;
+ struct pkcs7_signed_info *sinfo;
+
+ if (pkcs7) {
+ while (pkcs7->certs) {
+ cert = pkcs7->certs;
+ pkcs7->certs = cert->next;
+ x509_free_certificate(cert);
+ }
+ while (pkcs7->crl) {
+ cert = pkcs7->crl;
+ pkcs7->crl = cert->next;
+ x509_free_certificate(cert);
+ }
+ while (pkcs7->signed_infos) {
+ sinfo = pkcs7->signed_infos;
+ pkcs7->signed_infos = sinfo->next;
+ mpi_free(sinfo->sig.mpi[0]);
+ kfree(sinfo->sig.digest);
+ kfree(sinfo);
+ }
+ kfree(pkcs7);
+ }
+}
+EXPORT_SYMBOL_GPL(pkcs7_free_message);
+
+/**
+ * pkcs7_parse_message - Parse a PKCS#7 message
+ * @data: The raw binary ASN.1 encoded message to be parsed
+ * @datalen: The size of the encoded message
+ */
+struct pkcs7_message *pkcs7_parse_message(const void *data, size_t datalen)
+{
+ struct pkcs7_parse_context *ctx;
+ struct pkcs7_message *msg;
+ long ret;
+
+ ret = -ENOMEM;
+ msg = kzalloc(sizeof(struct pkcs7_message), GFP_KERNEL);
+ if (!msg)
+ goto error_no_sig;
+ ctx = kzalloc(sizeof(struct pkcs7_parse_context), GFP_KERNEL);
+ if (!ctx)
+ goto error_no_ctx;
+ ctx->sinfo = kzalloc(sizeof(struct pkcs7_signed_info), GFP_KERNEL);
+ if (!ctx->sinfo)
+ goto error_no_sinfo;
+
+ ctx->msg = msg;
+ ctx->data = (unsigned long)data;
+ ctx->ppcerts = &ctx->certs;
+ ctx->ppsinfo = &ctx->msg->signed_infos;
+
+ /* Attempt to decode the signature */
+ ret = asn1_ber_decoder(&pkcs7_decoder, ctx, data, datalen);
+ if (ret < 0)
+ goto error_decode;
+
+ while (ctx->certs) {
+ struct x509_certificate *cert = ctx->certs;
+ ctx->certs = cert->next;
+ x509_free_certificate(cert);
+ }
+ mpi_free(ctx->sinfo->sig.mpi[0]);
+ kfree(ctx->sinfo->sig.digest);
+ kfree(ctx->sinfo);
+ kfree(ctx);
+ return msg;
+
+error_decode:
+ mpi_free(ctx->sinfo->sig.mpi[0]);
+ kfree(ctx->sinfo->sig.digest);
+ kfree(ctx->sinfo);
+error_no_sinfo:
+ kfree(ctx);
+error_no_ctx:
+ pkcs7_free_message(msg);
+error_no_sig:
+ return ERR_PTR(ret);
+}
+EXPORT_SYMBOL_GPL(pkcs7_parse_message);
+
+/**
+ * pkcs7_get_content_data - Get access to the PKCS#7 content
+ * @pkcs7: The preparsed PKCS#7 message to access
+ * @_data: Place to return a pointer to the data
+ * @_data_len: Place to return the data length
+ * @want_wrapper: True if the ASN.1 object header should be included in the data
+ *
+ * Get access to the data content of the PKCS#7 message, including, optionally,
+ * the header of the ASN.1 object that contains it. Returns -ENODATA if the
+ * data object was missing from the message.
+ */
+int pkcs7_get_content_data(const struct pkcs7_message *pkcs7,
+ const void **_data, size_t *_data_len,
+ bool want_wrapper)
+{
+ size_t wrapper;
+
+ if (!pkcs7->data)
+ return -ENODATA;
+
+ wrapper = want_wrapper ? pkcs7->data_hdrlen : 0;
+ *_data = pkcs7->data - wrapper;
+ *_data_len = pkcs7->data_len + wrapper;
+ return 0;
+}
+EXPORT_SYMBOL_GPL(pkcs7_get_content_data);
+
+/*
+ * Note an OID when we find one for later processing when we know how
+ * to interpret it.
+ */
+int pkcs7_note_OID(void *context, size_t hdrlen,
+ unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct pkcs7_parse_context *ctx = context;
+
+ ctx->last_oid = look_up_OID(value, vlen);
+ if (ctx->last_oid == OID__NR) {
+ char buffer[50];
+ sprint_oid(value, vlen, buffer, sizeof(buffer));
+ printk("PKCS7: Unknown OID: [%lu] %s\n",
+ (unsigned long)value - ctx->data, buffer);
+ }
+ return 0;
+}
+
+/*
+ * Note the digest algorithm for the signature.
+ */
+int pkcs7_sig_note_digest_algo(void *context, size_t hdrlen,
+ unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct pkcs7_parse_context *ctx = context;
+
+ switch (ctx->last_oid) {
+ case OID_md4:
+ ctx->sinfo->sig.pkey_hash_algo = HASH_ALGO_MD4;
+ break;
+ case OID_md5:
+ ctx->sinfo->sig.pkey_hash_algo = HASH_ALGO_MD5;
+ break;
+ case OID_sha1:
+ ctx->sinfo->sig.pkey_hash_algo = HASH_ALGO_SHA1;
+ break;
+ case OID_sha256:
+ ctx->sinfo->sig.pkey_hash_algo = HASH_ALGO_SHA256;
+ break;
+ default:
+ printk("Unsupported digest algo: %u\n", ctx->last_oid);
+ return -ENOPKG;
+ }
+ return 0;
+}
+
+/*
+ * Note the public key algorithm for the signature.
+ */
+int pkcs7_sig_note_pkey_algo(void *context, size_t hdrlen,
+ unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct pkcs7_parse_context *ctx = context;
+
+ switch (ctx->last_oid) {
+ case OID_rsaEncryption:
+ ctx->sinfo->sig.pkey_algo = PKEY_ALGO_RSA;
+ break;
+ default:
+ printk("Unsupported pkey algo: %u\n", ctx->last_oid);
+ return -ENOPKG;
+ }
+ return 0;
+}
+
+/*
+ * Extract a certificate and store it in the context.
+ */
+int pkcs7_extract_cert(void *context, size_t hdrlen,
+ unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct pkcs7_parse_context *ctx = context;
+ struct x509_certificate *x509;
+
+ if (tag != ((ASN1_UNIV << 6) | ASN1_CONS_BIT | ASN1_SEQ)) {
+ pr_debug("Cert began with tag %02x at %lu\n",
+ tag, (unsigned long)ctx - ctx->data);
+ return -EBADMSG;
+ }
+
+ /* We have to correct for the header so that the X.509 parser can start
+ * from the beginning. Note that since X.509 stipulates DER, there
+ * probably shouldn't be an EOC trailer - but it is in PKCS#7 (which
+ * stipulates BER).
+ */
+ value -= hdrlen;
+ vlen += hdrlen;
+
+ if (((u8*)value)[1] == 0x80)
+ vlen += 2; /* Indefinite length - there should be an EOC */
+
+ x509 = x509_cert_parse(value, vlen);
+ if (IS_ERR(x509))
+ return PTR_ERR(x509);
+
+ pr_debug("Got cert for %s\n", x509->subject);
+ pr_debug("- fingerprint %s\n", x509->fingerprint);
+
+ x509->index = ++ctx->x509_index;
+ *ctx->ppcerts = x509;
+ ctx->ppcerts = &x509->next;
+ return 0;
+}
+
+/*
+ * Save the certificate list
+ */
+int pkcs7_note_certificate_list(void *context, size_t hdrlen,
+ unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct pkcs7_parse_context *ctx = context;
+
+ pr_devel("Got cert list (%02x)\n", tag);
+
+ *ctx->ppcerts = ctx->msg->certs;
+ ctx->msg->certs = ctx->certs;
+ ctx->certs = NULL;
+ ctx->ppcerts = &ctx->certs;
+ return 0;
+}
+
+/*
+ * Extract the data from the message and store that and its content type OID in
+ * the context.
+ */
+int pkcs7_note_data(void *context, size_t hdrlen,
+ unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct pkcs7_parse_context *ctx = context;
+
+ pr_debug("Got data\n");
+
+ ctx->msg->data = value;
+ ctx->msg->data_len = vlen;
+ ctx->msg->data_hdrlen = hdrlen;
+ ctx->msg->data_type = ctx->last_oid;
+ return 0;
+}
+
+/*
+ * Parse authenticated attributes
+ */
+int pkcs7_sig_note_authenticated_attr(void *context, size_t hdrlen,
+ unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct pkcs7_parse_context *ctx = context;
+
+ pr_devel("AuthAttr: %02x %zu [%*ph]\n", tag, vlen, (unsigned)vlen, value);
+
+ switch (ctx->last_oid) {
+ case OID_messageDigest:
+ if (tag != ASN1_OTS)
+ return -EBADMSG;
+ ctx->sinfo->msgdigest = value;
+ ctx->sinfo->msgdigest_len = vlen;
+ return 0;
+ default:
+ return 0;
+ }
+}
+
+/*
+ * Note the set of auth attributes for digestion purposes [RFC2315 9.3]
+ */
+int pkcs7_sig_note_set_of_authattrs(void *context, size_t hdrlen,
+ unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct pkcs7_parse_context *ctx = context;
+
+ /* We need to switch the 'CONT 0' to a 'SET OF' when we digest */
+ ctx->sinfo->authattrs = value - (hdrlen - 1);
+ ctx->sinfo->authattrs_len = vlen + (hdrlen - 1);
+ return 0;
+}
+
+/*
+ * Note the issuing certificate serial number
+ */
+int pkcs7_sig_note_serial(void *context, size_t hdrlen,
+ unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct pkcs7_parse_context *ctx = context;
+ ctx->sinfo->raw_serial = value;
+ ctx->sinfo->raw_serial_size = vlen;
+ return 0;
+}
+
+/*
+ * Note the issuer's name
+ */
+int pkcs7_sig_note_issuer(void *context, size_t hdrlen,
+ unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct pkcs7_parse_context *ctx = context;
+ ctx->sinfo->raw_issuer = value;
+ ctx->sinfo->raw_issuer_size = vlen;
+ return 0;
+}
+
+/*
+ * Note the signature data
+ */
+int pkcs7_sig_note_signature(void *context, size_t hdrlen,
+ unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct pkcs7_parse_context *ctx = context;
+ MPI mpi;
+
+ BUG_ON(ctx->sinfo->sig.pkey_algo != PKEY_ALGO_RSA);
+
+ mpi = mpi_read_raw_data(value, vlen);
+ if (!mpi)
+ return -ENOMEM;
+
+ ctx->sinfo->sig.mpi[0] = mpi;
+ ctx->sinfo->sig.nr_mpi = 1;
+ return 0;
+}
+
+/*
+ * Note a signature information block
+ */
+int pkcs7_note_signed_info(void *context, size_t hdrlen,
+ unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct pkcs7_parse_context *ctx = context;
+
+ ctx->sinfo->index = ++ctx->sinfo_index;
+ *ctx->ppsinfo = ctx->sinfo;
+ ctx->ppsinfo = &ctx->sinfo->next;
+ ctx->sinfo = kzalloc(sizeof(struct pkcs7_signed_info), GFP_KERNEL);
+ if (!ctx->sinfo)
+ return -ENOMEM;
+ return 0;
+}
diff --git a/crypto/asymmetric_keys/pkcs7_parser.h b/crypto/asymmetric_keys/pkcs7_parser.h
new file mode 100644
index 000000000000..d25f4d15370f
--- /dev/null
+++ b/crypto/asymmetric_keys/pkcs7_parser.h
@@ -0,0 +1,61 @@
+/* PKCS#7 crypto data parser internal definitions
+ *
+ * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#include <linux/oid_registry.h>
+#include <crypto/pkcs7.h>
+#include "x509_parser.h"
+
+#define kenter(FMT, ...) \
+ pr_devel("==> %s("FMT")\n", __func__, ##__VA_ARGS__)
+#define kleave(FMT, ...) \
+ pr_devel("<== %s()"FMT"\n", __func__, ##__VA_ARGS__)
+
+struct pkcs7_signed_info {
+ struct pkcs7_signed_info *next;
+ struct x509_certificate *signer; /* Signing certificate (in msg->certs) */
+ unsigned index;
+ bool trusted;
+
+ /* Message digest - the digest of the Content Data (or NULL) */
+ const void *msgdigest;
+ unsigned msgdigest_len;
+
+ /* Authenticated Attribute data (or NULL) */
+ unsigned authattrs_len;
+ const void *authattrs;
+
+ /* Issuing cert serial number and issuer's name */
+ const void *raw_serial;
+ unsigned raw_serial_size;
+ unsigned raw_issuer_size;
+ const void *raw_issuer;
+
+ /* Message signature.
+ *
+ * This contains the generated digest of _either_ the Content Data or
+ * the Authenticated Attributes [RFC2315 9.3]. If the latter, one of
+ * the attributes contains the digest of the the Content Data within
+ * it.
+ */
+ struct public_key_signature sig;
+};
+
+struct pkcs7_message {
+ struct x509_certificate *certs; /* Certificate list */
+ struct x509_certificate *crl; /* Revocation list */
+ struct pkcs7_signed_info *signed_infos;
+
+ /* Content Data (or NULL) */
+ enum OID data_type; /* Type of Data */
+ size_t data_len; /* Length of Data */
+ size_t data_hdrlen; /* Length of Data ASN.1 header */
+ const void *data; /* Content Data (or 0) */
+};