diff --git a/src/rspro/ber_decoder.c b/src/rspro/ber_decoder.c
new file mode 100644
index 0000000..0f99400
--- /dev/null
+++ b/src/rspro/ber_decoder.c
@@ -0,0 +1,283 @@
+/*-
+ * Copyright (c) 2003, 2004 Lev Walkin <vlm@lionet.info>. All rights reserved.
+ * Redistribution and modifications are permitted subject to BSD license.
+ */
+#include <asn_internal.h>
+
+#undef	ADVANCE
+#define	ADVANCE(num_bytes)	do {					\
+		size_t num = num_bytes;					\
+		ptr = ((const char *)ptr) + num;			\
+		size -= num;						\
+		consumed_myself += num;					\
+	} while(0)
+#undef	RETURN
+#define	RETURN(_code)	do {						\
+		asn_dec_rval_t rval;					\
+		rval.code = _code;					\
+		if(opt_ctx) opt_ctx->step = step; /* Save context */	\
+		if(_code == RC_OK || opt_ctx)				\
+			rval.consumed = consumed_myself;		\
+		else							\
+			rval.consumed = 0;	/* Context-free */	\
+		return rval;						\
+	} while(0)
+
+/*
+ * The BER decoder of any type.
+ */
+asn_dec_rval_t
+ber_decode(asn_codec_ctx_t *opt_codec_ctx,
+	asn_TYPE_descriptor_t *type_descriptor,
+	void **struct_ptr, const void *ptr, size_t size) {
+	asn_codec_ctx_t s_codec_ctx;
+
+	/*
+	 * Stack checker requires that the codec context
+	 * must be allocated on the stack.
+	 */
+	if(opt_codec_ctx) {
+		if(opt_codec_ctx->max_stack_size) {
+			s_codec_ctx = *opt_codec_ctx;
+			opt_codec_ctx = &s_codec_ctx;
+		}
+	} else {
+		/* If context is not given, be security-conscious anyway */
+		memset(&s_codec_ctx, 0, sizeof(s_codec_ctx));
+		s_codec_ctx.max_stack_size = _ASN_DEFAULT_STACK_MAX;
+		opt_codec_ctx = &s_codec_ctx;
+	}
+
+	/*
+	 * Invoke type-specific decoder.
+	 */
+	return type_descriptor->ber_decoder(opt_codec_ctx, type_descriptor,
+		struct_ptr,	/* Pointer to the destination structure */
+		ptr, size,	/* Buffer and its size */
+		0		/* Default tag mode is 0 */
+		);
+}
+
+/*
+ * Check the set of <TL<TL<TL...>>> tags matches the definition.
+ */
+asn_dec_rval_t
+ber_check_tags(asn_codec_ctx_t *opt_codec_ctx,
+		asn_TYPE_descriptor_t *td, asn_struct_ctx_t *opt_ctx,
+		const void *ptr, size_t size, int tag_mode, int last_tag_form,
+		ber_tlv_len_t *last_length, int *opt_tlv_form) {
+	ssize_t consumed_myself = 0;
+	ssize_t tag_len;
+	ssize_t len_len;
+	ber_tlv_tag_t tlv_tag;
+	ber_tlv_len_t tlv_len;
+	ber_tlv_len_t limit_len = -1;
+	int expect_00_terminators = 0;
+	int tlv_constr = -1;	/* If CHOICE, opt_tlv_form is not given */
+	int step = opt_ctx ? opt_ctx->step : 0;	/* Where we left previously */
+	int tagno;
+
+	/*
+	 * Make sure we didn't exceed the maximum stack size.
+	 */
+	if(_ASN_STACK_OVERFLOW_CHECK(opt_codec_ctx))
+		RETURN(RC_FAIL);
+
+	/*
+	 * So what does all this implicit skip stuff mean?
+	 * Imagine two types,
+	 * 	A ::= [5] IMPLICIT	T
+	 * 	B ::= [2] EXPLICIT	T
+	 * Where T is defined as
+	 *	T ::= [4] IMPLICIT SEQUENCE { ... }
+	 * 
+	 * Let's say, we are starting to decode type A, given the
+	 * following TLV stream: <5> <0>. What does this mean?
+	 * It means that the type A contains type T which is,
+	 * in turn, empty.
+	 * Remember though, that we are still in A. We cannot
+	 * just pass control to the type T decoder. Why? Because
+	 * the type T decoder expects <4> <0>, not <5> <0>.
+	 * So, we must make sure we are going to receive <5> while
+	 * still in A, then pass control to the T decoder, indicating
+	 * that the tag <4> was implicitly skipped. The decoder of T
+	 * hence will be prepared to treat <4> as valid tag, and decode
+	 * it appropriately.
+	 */
+
+	tagno = step	/* Continuing where left previously */
+		+ (tag_mode==1?-1:0)
+		;
+	ASN_DEBUG("ber_check_tags(%s, size=%ld, tm=%d, step=%d, tagno=%d)",
+		td->name, (long)size, tag_mode, step, tagno);
+	/* assert(td->tags_count >= 1) May not be the case for CHOICE or ANY */
+
+	if(tag_mode == 0 && tagno == td->tags_count) {
+		/*
+		 * This must be the _untagged_ ANY type,
+		 * which outermost tag isn't known in advance.
+		 * Fetch the tag and length separately.
+		 */
+		tag_len = ber_fetch_tag(ptr, size, &tlv_tag);
+		switch(tag_len) {
+		case -1: RETURN(RC_FAIL);
+		case 0: RETURN(RC_WMORE);
+		}
+		tlv_constr = BER_TLV_CONSTRUCTED(ptr);
+		len_len = ber_fetch_length(tlv_constr,
+			(const char *)ptr + tag_len, size - tag_len, &tlv_len);
+		switch(len_len) {
+		case -1: RETURN(RC_FAIL);
+		case 0: RETURN(RC_WMORE);
+		}
+		ASN_DEBUG("Advancing %ld in ANY case",
+			(long)(tag_len + len_len));
+		ADVANCE(tag_len + len_len);
+	} else {
+		assert(tagno < td->tags_count);	/* At least one loop */
+	}
+	for((void)tagno; tagno < td->tags_count; tagno++, step++) {
+
+		/*
+		 * Fetch and process T from TLV.
+		 */
+		tag_len = ber_fetch_tag(ptr, size, &tlv_tag);
+			ASN_DEBUG("Fetching tag from {%p,%ld}: "
+				"len %ld, step %d, tagno %d got %s",
+				ptr, (long)size,
+				(long)tag_len, step, tagno,
+				ber_tlv_tag_string(tlv_tag));
+		switch(tag_len) {
+		case -1: RETURN(RC_FAIL);
+		case 0: RETURN(RC_WMORE);
+		}
+
+		tlv_constr = BER_TLV_CONSTRUCTED(ptr);
+
+		/*
+		 * If {I}, don't check anything.
+		 * If {I,B,C}, check B and C unless we're at I.
+		 */
+		if(tag_mode != 0 && step == 0) {
+			/*
+			 * We don't expect tag to match here.
+			 * It's just because we don't know how the tag
+			 * is supposed to look like.
+			 */
+		} else {
+		    assert(tagno >= 0);	/* Guaranteed by the code above */
+		    if(tlv_tag != td->tags[tagno]) {
+			/*
+			 * Unexpected tag. Too bad.
+			 */
+		    	ASN_DEBUG("Expected: %s, "
+				"expectation failed (tn=%d, tm=%d)",
+				ber_tlv_tag_string(td->tags[tagno]),
+				tagno, tag_mode
+			);
+			RETURN(RC_FAIL);
+		    }
+		}
+
+		/*
+		 * Attention: if there are more tags expected,
+		 * ensure that the current tag is presented
+		 * in constructed form (it contains other tags!).
+		 * If this one is the last one, check that the tag form
+		 * matches the one given in descriptor.
+		 */
+		if(tagno < (td->tags_count - 1)) {
+			if(tlv_constr == 0) {
+				ASN_DEBUG("tlv_constr = %d, expfail",
+					tlv_constr);
+				RETURN(RC_FAIL);
+			}
+		} else {
+			if(last_tag_form != tlv_constr
+			&& last_tag_form != -1) {
+				ASN_DEBUG("last_tag_form %d != %d",
+					last_tag_form, tlv_constr);
+				RETURN(RC_FAIL);
+			}
+		}
+
+		/*
+		 * Fetch and process L from TLV.
+		 */
+		len_len = ber_fetch_length(tlv_constr,
+			(const char *)ptr + tag_len, size - tag_len, &tlv_len);
+		ASN_DEBUG("Fetching len = %ld", (long)len_len);
+		switch(len_len) {
+		case -1: RETURN(RC_FAIL);
+		case 0: RETURN(RC_WMORE);
+		}
+
+		/*
+		 * FIXME
+		 * As of today, the chain of tags
+		 * must either contain several indefinite length TLVs,
+		 * or several definite length ones.
+		 * No mixing is allowed.
+		 */
+		if(tlv_len == -1) {
+			/*
+			 * Indefinite length.
+			 */
+			if(limit_len == -1) {
+				expect_00_terminators++;
+			} else {
+				ASN_DEBUG("Unexpected indefinite length "
+					"in a chain of definite lengths");
+				RETURN(RC_FAIL);
+			}
+			ADVANCE(tag_len + len_len);
+			continue;
+		} else {
+			if(expect_00_terminators) {
+				ASN_DEBUG("Unexpected definite length "
+					"in a chain of indefinite lengths");
+				RETURN(RC_FAIL);
+			}
+		}
+
+		/*
+		 * Check that multiple TLVs specify ever decreasing length,
+		 * which is consistent.
+		 */
+		if(limit_len == -1) {
+			limit_len    = tlv_len + tag_len + len_len;
+			if(limit_len < 0) {
+				/* Too great tlv_len value? */
+				RETURN(RC_FAIL);
+			}
+		} else if(limit_len != tlv_len + tag_len + len_len) {
+			/*
+			 * Inner TLV specifies length which is inconsistent
+			 * with the outer TLV's length value.
+			 */
+			ASN_DEBUG("Outer TLV is %ld and inner is %ld",
+				(long)limit_len, (long)tlv_len);
+			RETURN(RC_FAIL);
+		}
+
+		ADVANCE(tag_len + len_len);
+
+		limit_len -= (tag_len + len_len);
+		if((ssize_t)size > limit_len) {
+			/*
+			 * Make sure that we won't consume more bytes
+			 * from the parent frame than the inferred limit.
+			 */
+			size = limit_len;
+		}
+	}
+
+	if(opt_tlv_form)
+		*opt_tlv_form = tlv_constr;
+	if(expect_00_terminators)
+		*last_length = -expect_00_terminators;
+	else
+		*last_length = tlv_len;
+
+	RETURN(RC_OK);
+}