--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/nss/lib/util/derdec.c	Mon Jul 28 10:47:06 2014 +0200
@@ -0,0 +1,189 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "secder.h"
+#include "secerr.h"
+
+static PRUint32
+der_indefinite_length(unsigned char *buf, unsigned char *end)
+{
+    PRUint32 len, ret, dataLen;
+    unsigned char tag, lenCode;
+    int dataLenLen;
+
+    len = 0;
+    while ( 1 ) {
+	if ((buf + 2) > end) {
+	    return(0);
+	}
+	
+	tag = *buf++;
+	lenCode = *buf++;
+	len += 2;
+	
+	if ( ( tag == 0 ) && ( lenCode == 0 ) ) {
+	    return(len);
+	}
+	
+	if ( lenCode == 0x80 ) {	/* indefinite length */
+	    ret = der_indefinite_length(buf, end); /* recurse to find length */
+	    if (ret == 0)
+		return 0;
+	    len += ret;
+	    buf += ret;
+	} else {			/* definite length */
+	    if (lenCode & 0x80) {
+		/* Length of data is in multibyte format */
+		dataLenLen = lenCode & 0x7f;
+		switch (dataLenLen) {
+		  case 1:
+		    dataLen = buf[0];
+		    break;
+		  case 2:
+		    dataLen = (buf[0]<<8)|buf[1];
+		    break;
+		  case 3:
+		    dataLen = ((unsigned long)buf[0]<<16)|(buf[1]<<8)|buf[2];
+		    break;
+		  case 4:
+		    dataLen = ((unsigned long)buf[0]<<24)|
+			((unsigned long)buf[1]<<16)|(buf[2]<<8)|buf[3];
+		    break;
+		  default:
+		    PORT_SetError(SEC_ERROR_BAD_DER);
+		    return SECFailure;
+		}
+	    } else {
+		/* Length of data is in single byte */
+		dataLen = lenCode;
+		dataLenLen = 0;
+	    }
+
+	    /* skip this item */
+	    buf = buf + dataLenLen + dataLen;
+	    len = len + dataLenLen + dataLen;
+	}
+    }
+}
+
+/*
+** Capture the next thing in the buffer.
+** Returns the length of the header and the length of the contents.
+*/
+static SECStatus
+der_capture(unsigned char *buf, unsigned char *end,
+	    int *header_len_p, PRUint32 *contents_len_p)
+{
+    unsigned char *bp;
+    unsigned char whole_tag;
+    PRUint32 contents_len;
+    int tag_number;
+
+    if ((buf + 2) > end) {
+	*header_len_p = 0;
+	*contents_len_p = 0;
+	if (buf == end)
+	    return SECSuccess;
+	return SECFailure;
+    }
+
+    bp = buf;
+
+    /* Get tag and verify that it is ok. */
+    whole_tag = *bp++;
+    tag_number = whole_tag & DER_TAGNUM_MASK;
+
+    /*
+     * XXX This code does not (yet) handle the high-tag-number form!
+     */
+    if (tag_number == DER_HIGH_TAG_NUMBER) {
+	PORT_SetError(SEC_ERROR_BAD_DER);
+	return SECFailure;
+    }
+
+    if ((whole_tag & DER_CLASS_MASK) == DER_UNIVERSAL) {
+	/* Check that the universal tag number is one we implement.  */
+	switch (tag_number) {
+	  case DER_BOOLEAN:
+	  case DER_INTEGER:
+	  case DER_BIT_STRING:
+	  case DER_OCTET_STRING:
+	  case DER_NULL:
+	  case DER_OBJECT_ID:
+	  case DER_SEQUENCE:
+	  case DER_SET:
+	  case DER_PRINTABLE_STRING:
+	  case DER_T61_STRING:
+	  case DER_IA5_STRING:
+	  case DER_VISIBLE_STRING:
+	  case DER_UTC_TIME:
+	  case 0:			/* end-of-contents tag */
+	    break;
+	  default:
+	    PORT_SetError(SEC_ERROR_BAD_DER);
+	    return SECFailure;
+	}
+    }
+
+    /*
+     * Get first byte of length code (might contain entire length, might not).
+     */
+    contents_len = *bp++;
+
+    /*
+     * If the high bit is set, then the length is in multibyte format,
+     * or the thing has an indefinite-length.
+     */
+    if (contents_len & 0x80) {
+	int bytes_of_encoded_len;
+
+	bytes_of_encoded_len = contents_len & 0x7f;
+	contents_len = 0;
+
+	switch (bytes_of_encoded_len) {
+	  case 4:
+	    contents_len |= *bp++;
+	    contents_len <<= 8;
+	    /* fallthru */
+	  case 3:
+	    contents_len |= *bp++;
+	    contents_len <<= 8;
+	    /* fallthru */
+	  case 2:
+	    contents_len |= *bp++;
+	    contents_len <<= 8;
+	    /* fallthru */
+	  case 1:
+	    contents_len |= *bp++;
+	    break;
+
+	  case 0:
+	    contents_len = der_indefinite_length (bp, end);
+	    if (contents_len)
+		break;
+	    /* fallthru */
+	  default:
+	    PORT_SetError(SEC_ERROR_BAD_DER);
+	    return SECFailure;
+	}
+    }
+
+    if ((bp + contents_len) > end) {
+	/* Ran past end of buffer */
+	PORT_SetError(SEC_ERROR_BAD_DER);
+	return SECFailure;
+    }
+
+    *header_len_p = bp - buf;
+    *contents_len_p = contents_len;
+
+    return SECSuccess;
+}
+
+SECStatus
+DER_Lengths(SECItem *item, int *header_len_p, PRUint32 *contents_len_p)
+{
+    return(der_capture(item->data, &item->data[item->len], header_len_p,
+		       contents_len_p));
+}