[apple/security.git] / OSX / libsecurity_keychain / libDER / libDER / DER_Decode.c

/*
 * Copyright (c) 2005-2017 Apple Inc. All Rights Reserved.
 * 
 * @APPLE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this
 * file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */

/* 
 * DER_Decode.c - DER decoding routines
 */
 
#include <libDER/DER_Decode.h>
#include <libDER/asn1Types.h>

#include <libDER/libDER_config.h>

#ifndef DER_DECODE_ENABLE
#error Please define DER_DECODE_ENABLE.
#endif

#if             DER_DECODE_ENABLE

#define DER_DECODE_DEBUG        0
#if             DER_DECODE_DEBUG
#include <stdio.h>
#define derDecDbg(a)                    printf(a)
#define derDecDbg1(a, b)                printf(a, b)
#define derDecDbg2(a, b, c)             printf(a, b, c)
#define derDecDbg3(a, b, c, d)  printf(a, b, c, d)
#else   
#define derDecDbg(a)    
#define derDecDbg1(a, b)        
#define derDecDbg2(a, b, c)     
#define derDecDbg3(a, b, c, d)
#endif  /* DER_DECODE_DEBUG */

/*
 *  Basic decoding primitive. Only works with:
 *
 *  -- definite length encoding
 *  -- one-byte tags (unless DER_MULTIBYTE_TAGS is defined)
 *  -- max content length fits in a DERSize
 *
 * No malloc or copy of the contents is performed; the returned
 * content->content.data is a pointer into the incoming der data.
 */
DERReturn DERDecodeItem(
                        const DERItem        *der,                        /* data to decode */
                        DERDecodedInfo        *decoded)                /* RETURNED */
{
    return DERDecodeItemPartialBufferGetLength(der, decoded, NULL);
}

/*
 *  Basic decoding primitive. Allows for decoding with a partial buffer.
 *  if allowPartialBuffer is true. A partial buffer would normally fail
 *  because the encoded length would be greater than the size of the buffer passed in.
 *  Only works with:
 *
 *  -- definite length encoding
 *  -- one-byte tags (unless DER_MULTIBYTE_TAGS is defined)
 *  -- max content length fits in a DERSize
 *
 * No malloc or copy of the contents is performed; the returned
 * content->content.data is a pointer into the incoming der data.
 *
 * WARNING: Using a partial buffer can return a DERDecodedInfo object with
 * a length larger than the buffer.  It is recommended to instead use
 * DERDecodeItemPartialBufferGetLength if you need partial buffers.
 *
 */
DERReturn DERDecodeItemPartialBuffer(
        const DERItem   *der,                   /* data to decode */
        DERDecodedInfo  *decoded,               /* RETURNED */
    bool allowPartialBuffer)
{
    DERByte tag1;                        /* first tag byte */
    DERByte len1;                        /* first length byte */
    DERTag tagNumber;       /* tag number without class and method bits */
    DERByte *derPtr = der->data;
    DERSize derLen = der->length;

    /* The tag decoding below is fully BER complient.  We support a max tag
     value of 2 ^ ((sizeof(DERTag) * 8) - 3) - 1 so for tag size 1 byte we
     support tag values from 0 - 0x1F.  For tag size 2 tag values
     from 0 - 0x1FFF and for tag size 4 values from 0 - 0x1FFFFFFF. */
    if(derLen < 2) {
        return DR_DecodeError;
    }
    /* Grab the first byte of the tag. */
    tag1 = *derPtr++;
    derLen--;
    tagNumber = tag1 & 0x1F;
    if(tagNumber == 0x1F) {
#ifdef DER_MULTIBYTE_TAGS
        /* Long tag form: bit 8 of each octet shall be set to one unless it is
         the last octet of the tag */
        const DERTag overflowMask = ((DERTag)0x7F << (sizeof(DERTag) * 8 - 7));
        DERByte tagByte;
        tagNumber = 0;
        if (*derPtr == 0x80 || *derPtr < 0x1F)
            return DR_DecodeError;
        do {
            if(derLen < 2 || (tagNumber & overflowMask) != 0) {
                return DR_DecodeError;
            }
            tagByte = *derPtr++;
            derLen--;
            tagNumber = (tagNumber << 7) | (tagByte & 0x7F);
        } while((tagByte & 0x80) != 0);

        /* Check for any of the top 3 reserved bits being set. */
        if ((tagNumber & (overflowMask << 4)) != 0)
#endif
            return DR_DecodeError;
    }
    /* Returned tag, top 3 bits are class/method remaining bits are number. */
    decoded->tag = ((DERTag)(tag1 & 0xE0) << ((sizeof(DERTag) - 1) * 8)) | tagNumber;

    /* Tag decoding above ensured we have at least one more input byte left. */
    len1 = *derPtr++;
    derLen--;
    if(len1 & 0x80) {
        /* long length form - first byte is length of length */
        DERSize longLen = 0;        /* long form length */

        unsigned dex;
        len1 &= 0x7f;
        if((len1 > sizeof(DERSize)) || (len1 > derLen) || len1 == 0 || *derPtr == 0) {
            /* no can do */
            return DR_DecodeError;
        }
        for(dex=0; dex<len1; dex++) {
            longLen <<= 8;
            longLen |= *derPtr++;
            derLen--;
        }
        if(longLen > derLen && !allowPartialBuffer) {
            /* not enough data left for this encoding */
            return DR_DecodeError;
        }
        decoded->content.data = derPtr;
        decoded->content.length = longLen;
    }
    else {
        /* short length form, len1 is the length */
        if(len1 > derLen && !allowPartialBuffer) {
            /* not enough data left for this encoding */
            return DR_DecodeError;
        }
        decoded->content.data = derPtr;
        decoded->content.length = len1;
    }

    return DR_Success;
}

/*
 * Same as above, but returns a DERDecodedInfo with a length no larger than the buffer.
 * The actual encoded length can be retrieved from encodedLength parameter.
 * encodedLength can be NULL to achieve the same behavior as DERDecodeItemPartialBuffer,
 * with allowPartialBuffer=false
 *
 * NOTE: The DERDecoded length will never be larger than the input buffer.
 * This is a key difference from DERDecodeItemPartialBuffer which could return invalid length.
 *
 */
DERReturn DERDecodeItemPartialBufferGetLength(
    const DERItem       *der,                   /* data to decode */
    DERDecodedInfo      *decoded,       /* RETURNED */
    DERSize         *encodedLength)
{
    DERByte tag1;                       /* first tag byte */
    DERByte len1;                       /* first length byte */
    DERTag tagNumber;       /* tag number without class and method bits */
    DERByte *derPtr = der->data;
    DERSize derLen = der->length;

    /* The tag decoding below is fully BER complient.  We support a max tag
     value of 2 ^ ((sizeof(DERTag) * 8) - 3) - 1 so for tag size 1 byte we
     support tag values from 0 - 0x1F.  For tag size 2 tag values
     from 0 - 0x1FFF and for tag size 4 values from 0 - 0x1FFFFFFF. */
    if(derLen < 2) {
        return DR_DecodeError;
    }
    /* Grab the first byte of the tag. */
    tag1 = *derPtr++;
    derLen--;
    tagNumber = tag1 & 0x1F;
    if(tagNumber == 0x1F) {
#ifdef DER_MULTIBYTE_TAGS
        /* Long tag form: bit 8 of each octet shall be set to one unless it is
         the last octet of the tag */
        const DERTag overflowMask = ((DERTag)0x7F << (sizeof(DERTag) * 8 - 7));
        DERByte tagByte;
        tagNumber = 0;
        if (*derPtr == 0x80 || *derPtr < 0x1F)
            return DR_DecodeError;
        do {
            if(derLen < 2 || (tagNumber & overflowMask) != 0) {
                return DR_DecodeError;
            }
            tagByte = *derPtr++;
            derLen--;
            tagNumber = (tagNumber << 7) | (tagByte & 0x7F);
        } while((tagByte & 0x80) != 0);

        /* Check for any of the top 3 reserved bits being set. */
        if ((tagNumber & (overflowMask << 4)) != 0)
#endif
            return DR_DecodeError;
    }
    /* Returned tag, top 3 bits are class/method remaining bits are number. */
    decoded->tag = ((DERTag)(tag1 & 0xE0) << ((sizeof(DERTag) - 1) * 8)) | tagNumber;

    /* Tag decoding above ensured we have at least one more input byte left. */
    len1 = *derPtr++;
    derLen--;
    if(len1 & 0x80) {
        /* long length form - first byte is length of length */
        DERSize longLen = 0;    /* long form length */
        unsigned dex;

        len1 &= 0x7f;
        if((len1 > sizeof(DERSize)) || (len1 > derLen) || len1 == 0 || *derPtr == 0) {
            /* no can do */
            return DR_DecodeError;
        }
        for(dex=0; dex<len1; dex++) {
            longLen <<= 8;
            longLen |= *derPtr++;
            derLen--;
        }
        if(longLen > derLen && !encodedLength) {
            /* not enough data left for this encoding */
            return DR_DecodeError;
        }
        if (longLen<derLen) {
            derLen = longLen;
        }
        decoded->content.data = derPtr;
        decoded->content.length = derLen;
        if (encodedLength) {
            *encodedLength = longLen;
        }
    }
    else {
        /* short length form, len1 is the length */
        if(len1 > derLen && !encodedLength) {
            /* not enough data left for this encoding */
            return DR_DecodeError;
        }
        if (len1<derLen) {
            derLen=len1;
        }
        decoded->content.data = derPtr;
        decoded->content.length = derLen;
        if (encodedLength) {
            *encodedLength = len1;
        }
    }

    return DR_Success;
}

/*
 * Given a BIT_STRING, in the form of its raw content bytes,
 * obtain the number of unused bits and the raw bit string bytes.
 */
DERReturn DERParseBitString(
        const DERItem   *contents,
        DERItem                 *bitStringBytes,        /* RETURNED */
        DERByte                 *numUnusedBits)         /* RETURNED */
{
        if(contents->length < 2) {
                /* not enough room for actual bits after the unused bits field */
                *numUnusedBits = 0;
                bitStringBytes->data = NULL;
                bitStringBytes->length = 0;
                return DR_Success;
        }
        *numUnusedBits = contents->data[0];
        bitStringBytes->data = contents->data + 1;
        bitStringBytes->length = contents->length - 1;
        return DR_Success;
}

/* 
 * Given a BOOLEAN, in the form of its raw content bytes, 
 * obtain it's value.
 */
DERReturn DERParseBoolean(
        const DERItem   *contents,
        bool                    *value) {       /* RETURNED */
    if (contents->length != 1 ||
        (contents->data[0] != 0 && contents->data[0] != 0xFF))
        return DR_DecodeError;

    *value = contents->data[0] != 0;
    return DR_Success;
}

/*
 * Given a BOOLEAN, in the form of its raw content bytes,
 * obtain it's value.
 */
DERReturn DERParseBooleanWithDefault(
    const DERItem       *contents,
    bool                        defaultValue,
    bool                        *value) {       /* RETURNED */
    if (contents->length == 0) {
        *value = defaultValue;
        return DR_Success;
    }
    return DERParseBoolean(contents, value);
}


DERReturn DERParseInteger(
                          const DERItem        *contents,
                          uint32_t        *result) {        /* RETURNED */
    uint64_t value;
    DERReturn drtn = DERParseInteger64(contents, &value);
    if (drtn == DR_Success) {
        if (value > UINT32_MAX)
            drtn = DR_BufOverflow;
        else
            *result = (uint32_t)value;
    }
    return drtn;
}

DERReturn DERParseInteger64(
                            const DERItem        *contents,
                            uint64_t        *result) {        /* RETURNED */
    DERSize ix, length = contents->length;
    if (length == 0)
        return DR_DecodeError;
    if (contents->data[0] & 0x80)
        return DR_DecodeError;
    if (contents->data[0] == 0) {
        if (length > 1 && (contents->data[1] & 0x80) == 0)
            return DR_DecodeError;
        if (length > sizeof(*result) + 1)
            return DR_BufOverflow;
    } else if (length > sizeof(*result)) {
        return DR_BufOverflow;
    }
    uint64_t value = 0;
    for (ix = 0; ix < length; ++ix) {
        value <<= 8;
        value += contents->data[ix];
    }
    *result = value;
    return DR_Success;
}

/* Sequence/set support */

/* 
 * To decode a set or sequence, call DERDecodeSeqInit once, then
 * call DERDecodeSeqNext to get each enclosed item.
 * DERDecodeSeqNext returns DR_EndOfSequence when no more
 * items are available. 
 */
DERReturn DERDecodeSeqInit(
        const DERItem   *der,                   /* data to decode */
        DERTag                  *tag,                   /* RETURNED tag of sequence/set. This will be
                                                                         * either ASN1_CONSTR_SEQUENCE or ASN1_CONSTR_SET. */
        DERSequence             *derSeq)                /* RETURNED, to use in DERDecodeSeqNext */
{
        DERDecodedInfo decoded;
        DERReturn drtn;
        
        drtn = DERDecodeItem(der, &decoded);
        if(drtn) {
                return drtn;
        }
    *tag = decoded.tag;
        switch(decoded.tag) {
                case ASN1_CONSTR_SEQUENCE:
                case ASN1_CONSTR_SET:
                        break;
                default:
                        return DR_UnexpectedTag;
        }
        derSeq->nextItem = decoded.content.data;
        derSeq->end = decoded.content.data + decoded.content.length;
        return DR_Success;
}

/* 
 * Use this to start in on decoding a sequence's content, when 
 * the top-level tag and content have already been decoded. 
 */
DERReturn DERDecodeSeqContentInit(
        const DERItem   *content,
        DERSequence             *derSeq)                /* RETURNED, to use in DERDecodeSeqNext */
{
        /* just prepare for decoding items in content */
        derSeq->nextItem = content->data;
        derSeq->end = content->data + content->length;
        return DR_Success;
}

DERReturn DERDecodeSeqNext(
        DERSequence             *derSeq,
        DERDecodedInfo  *decoded)               /* RETURNED */
{
        DERReturn drtn;
        DERItem item;
        
        if(derSeq->nextItem >= derSeq->end) {
                /* normal termination, contents all used up */
                return DR_EndOfSequence;
        }
        
        /* decode next item */
        item.data = derSeq->nextItem;
        item.length = (DERSize) (derSeq->end - derSeq->nextItem);
        drtn = DERDecodeItem(&item, decoded);
        if(drtn) {
                return drtn;
        }       
        
        /* skip over the item we just decoded */
        derSeq->nextItem = decoded->content.data + decoded->content.length;
        return DR_Success;
}

/* 
 * High level sequence parse, starting with top-level tag and content.
 * Top level tag must be ASN1_CONSTR_SEQUENCE - if it's not, and that's 
 * OK, use DERParseSequenceContent().
 */
DERReturn DERParseSequence(
        const DERItem                   *der,
        DERShort                                numItems,       /* size of itemSpecs[] */
        const DERItemSpec               *itemSpecs,
        void                                    *dest,          /* DERDecodedInfo(s) here RETURNED */
        DERSize                                 sizeToZero)     /* optional */
{
        DERReturn drtn;
        DERDecodedInfo topDecode;
        
        drtn = DERDecodeItem(der, &topDecode);
        if(drtn) {
                return drtn;
        }
        if(topDecode.tag != ASN1_CONSTR_SEQUENCE) {
                return DR_UnexpectedTag;
        }
        return DERParseSequenceContent(&topDecode.content,
                numItems, itemSpecs, dest, sizeToZero);
}

/* high level sequence parse, starting with sequence's content */
DERReturn DERParseSequenceContent(
        const DERItem                   *content,
        DERShort                                numItems,       /* size of itemSpecs[] */
        const DERItemSpec               *itemSpecs,
        void                                    *dest,          /* DERDecodedInfo(s) here RETURNED */
        DERSize                                 sizeToZero)     /* optional */
{
        DERSequence                     derSeq;
        DERReturn                       drtn;
        DERShort                        itemDex;
        DERByte                         *currDER;       /* full DER encoding of current item */
        
        if(sizeToZero) {
                DERMemset(dest, 0, sizeToZero);
        }
        
        drtn = DERDecodeSeqContentInit(content, &derSeq);
        if(drtn) {
                return drtn;
        }
        
        /* main loop */
        for(itemDex=0 ; itemDex<numItems; ) {
                DERDecodedInfo currDecoded;
                DERShort i;
                DERTag foundTag;
                char foundMatch = 0;
                
                /* save this in case of DER_DEC_SAVE_DER */
                currDER = derSeq.nextItem;
                
                drtn = DERDecodeSeqNext(&derSeq, &currDecoded);
                if(drtn) {
                        /* 
                         * One legal error here is DR_EndOfSequence when 
                         * all remaining DERSequenceItems are optional. 
                         */
                        if(drtn == DR_EndOfSequence) {
                                for(i=itemDex; i<numItems; i++) {
                                        if(!(itemSpecs[i].options & DER_DEC_OPTIONAL)) {
                                                /* unexpected end of sequence */
                                                return DR_IncompleteSeq;
                                        }
                                }
                                /* the rest are optional; success */
                                return DR_Success;
                        }
                        else {
                                /* any other error is fatal */
                                return drtn;
                        }
                }       /* decode error */
                
                /* 
                 * Seek matching tag or ASN_ANY in itemSpecs, skipping 
                 * over optional items.
                 */
                foundTag = currDecoded.tag;
                derDecDbg1("--- foundTag 0x%llx\n", foundTag);
                
                for(i=itemDex; i<numItems; i++) {
                        const DERItemSpec *currItemSpec = &itemSpecs[i];
                        DERShort currOptions = currItemSpec->options;
                        derDecDbg3("--- currItem %u expectTag 0x%llx currOptions 0x%x\n",
                                i, currItemSpec->tag, currOptions);
                        
                        if((currOptions & DER_DEC_ASN_ANY) ||
                           (foundTag == currItemSpec->tag)) {
                                /* 
                                 * We're good with this one. Cook up destination address
                                 * as appropriate. 
                                 */
                                if(!(currOptions & DER_DEC_SKIP)) {
                                        derDecDbg1("--- MATCH at currItem %u\n", i);
                                        DERByte *byteDst = (DERByte *)dest + currItemSpec->offset;
                                        DERItem *dst = (DERItem *)byteDst;
                                        *dst = currDecoded.content;
                                        if(currOptions & DER_DEC_SAVE_DER) {
                                                /* recreate full DER encoding of this item */
                                                derDecDbg1("--- SAVE_DER at currItem %u\n", i);
                                                dst->data = currDER;
                                                dst->length += (currDecoded.content.data - currDER);
                                        }
                                }

                                /* on to next item */
                                itemDex = i + 1;
                                
                                /* is this the end? */
                                if(itemDex == numItems) {
                                        /* normal termination if we consumed everything */
                                        if (currDecoded.content.data + currDecoded.content.length == content->data + content->length)
                                                return DR_Success;
                                        else
                                                return DR_DecodeError;
                                }
                                else {
                                        /* on to next item */ 
                                        foundMatch = 1;
                                        break;
                                }
                        } /* ASN_ANY, or match */
                        
                        /* 
                         * If current itemSpec isn't optional, abort - else on to 
                         * next item
                         */
                        if(!(currOptions & DER_DEC_OPTIONAL)) {
                                derDecDbg1("--- MISMATCH at currItem %u, !OPTIONAL, abort\n", i);
                                return DR_UnexpectedTag;
                        }
                        
                        /* else this was optional, on to next item */
                } /* searching for tag match */
                
                if(foundMatch == 0) {
                        /* 
                         * Found an item we couldn't match to any tag spec and we're at
                         * the end. 
                         */
                        derDecDbg("--- TAG NOT FOUND, abort\n");
                        return DR_UnexpectedTag;
                }
                
                /* else on to next item */
        }       /* main loop */
        
    /* Template has 0 items if we get here. */
    /* normal termination if we consumed everything, (the sequence was empty) */
    if (derSeq.nextItem == derSeq.end)
        return DR_Success;
    else
        return DR_DecodeError;
}

#if 0
/* 
 * High level sequence parse, starting with top-level tag and content.
 * Top level tag must be ASN1_CONSTR_SEQUENCE - if it's not, and that's 
 * OK, use DERParseSequenceContent().
 */
DERReturn DERParseSequenceOf(
        const DERItem                   *der,
        DERShort                                numItems,       /* size of itemSpecs[] */
        const DERItemSpec               *itemSpecs,
        void                                    *dest,          /* DERDecodedInfo(s) here RETURNED */
        DERSize                                 *numDestItems)  /* output */
{
        DERReturn drtn;
        DERDecodedInfo topDecode;
        
        drtn = DERDecodeItem(der, &topDecode);
        if(drtn) {
                return drtn;
        }
        if(topDecode.tag != ASN1_CONSTR_SEQUENCE) {
                return DR_UnexpectedTag;
        }
        return DERParseSequenceContent(&topDecode.content,
                numItems, itemSpecs, dest, sizeToZero);
}

/* 
 * High level set of parse, starting with top-level tag and content.
 * Top level tag must be ASN1_CONSTR_SET - if it's not, and that's 
 * OK, use DERParseSetOrSequenceOfContent().
 */
DERReturn DERParseSetOf(
        const DERItem                   *der,
        DERShort                                numItems,       /* size of itemSpecs[] */
        const DERItemSpec               *itemSpecs,
        void                                    *dest,          /* DERDecodedInfo(s) here RETURNED */
        DERSize                                 *numDestItems)  /* output */
{
        DERReturn drtn;
        DERDecodedInfo topDecode;
        
        drtn = DERDecodeItem(der, &topDecode);
        if(drtn) {
                return drtn;
        }
        if(topDecode.tag != ASN1_CONSTR_SET) {
                return DR_UnexpectedTag;
        }
        return DERParseSetOrSequenceOfContent(&topDecode.content,
                numItems, itemSpecs, dest, numDestItems);
}

/* High level set of or sequence of parse, starting with set or
   sequence's content */
DERReturn DERParseSetOrSequenceOfContent(
    const DERItem                       *content,
    void(*itemHandeler)(void *, const DERDecodedInfo *)
        void                                    *itemHandelerContext);
{
    DERSequence                 derSeq;
    DERShort                    itemDex;

    drtn = DERDecodeSeqContentInit(content, &derSeq);
    require_noerr_quiet(drtn, badCert);

    /* main loop */
    for (;;) {
        DERDecodedInfo currDecoded;
        DERShort i;
        DERByte foundTag;
        char foundMatch = 0;

        drtn = DERDecodeSeqNext(&derSeq, &currDecoded);
        if(drtn) {
            /* The only legal error here is DR_EndOfSequence. */
            if(drtn == DR_EndOfSequence) {
                /* no more items left in the sequence; success */
                return DR_Success;
            }
            else {
                /* any other error is fatal */
                require_noerr_quiet(drtn, badCert);
            }
        }       /* decode error */
        
        /* Each element can be anything. */
        foundTag = currDecoded.tag;

        /* 
         * We're good with this one. Cook up destination address
         * as appropriate. 
         */
        DERByte *byteDst = (DERByte *)dest + currItemSpec->offset;
        DERItem *dst = (DERItem *)byteDst;
        *dst = currDecoded.content;
        if(currOptions & DER_DEC_SAVE_DER) {
            /* recreate full DER encoding of this item */
            derDecDbg1("--- SAVE_DER at currItem %u\n", i);
            dst->data = currDER;
            dst->length += (currDecoded.content.data - currDER);
        }

        /* on to next item */
        itemDex = i + 1;
        
        /* is this the end? */
        if(itemDex == numItems) {
            /* normal termination */
            return DR_Success;
        }
        else {
            /* on to next item */ 
            foundMatch = 1;
            break;
        }
            
            /* 
             * If current itemSpec isn't optional, abort - else on to 
             * next item
             */
            if(!(currOptions & DER_DEC_OPTIONAL)) {
                derDecDbg1("--- MISMATCH at currItem %u, !OPTIONAL, abort\n", i);
                return DR_UnexpectedTag;
            }
            
            /* else this was optional, on to next item */
        } /* searching for tag match */
        
        if(foundMatch == 0) {
            /* 
             * Found an item we couldn't match to any tag spec and we're at
             * the end. 
             */
            derDecDbg("--- TAG NOT FOUND, abort\n");
            return DR_UnexpectedTag;
        }
        
        /* else on to next item */
    }   /* main loop */

    /*
     * If we get here, there appears to be more to process, but we've
     * given the caller everything they want. 
     */
    return DR_Success;
    }
}
#endif

#endif  /* DER_DECODE_ENABLE */