pkcs7: add support for signed data

OpenSSL provides APIs to generate only the signted data
format PKCS7 i.e. without content type OID. This patch
adds support to parse the data correctly even if formatted
only as signed data

Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
diff --git a/tests/data_files/Makefile b/tests/data_files/Makefile
index 288b01f..dbe3234 100644
--- a/tests/data_files/Makefile
+++ b/tests/data_files/Makefile
@@ -1223,6 +1223,11 @@
 	echo -en '\x15' | dd of=$@ seek=973 bs=1 conv=notrunc
 all_final += pkcs7_signerInfo_serial_invalid_size.der
 
+# pkcs7 signature file just with signed data
+pkcs7_data_cert_signeddata_sha256.der: pkcs7_data_cert_signed_sha256.der
+	dd if=pkcs7_data_cert_signed_sha256.der of=$@ skip=19 bs=1
+all_final += pkcs7_data_cert_signeddata_sha256.der
+
 ################################################################
 #### Diffie-Hellman parameters
 ################################################################