/* $OpenBSD: bs_ber.c,v 1.2 2015/02/06 22:22:33 doug Exp $ */ /* * Copyright (c) 2014, Google Inc. * * Permission to use, copy, modify, and/or distribute this software for any * purpose with or without fee is hereby granted, provided that the above * copyright notice and this permission notice appear in all copies. * * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */ #include #include #include "bytestring.h" /* * kMaxDepth is a just a sanity limit. The code should be such that the length * of the input being processes always decreases. None the less, a very large * input could otherwise cause the stack to overflow. */ static const unsigned kMaxDepth = 2048; /* * cbs_find_ber walks an ASN.1 structure in |orig_in| and sets |*ber_found| * depending on whether an indefinite length element was found. The value of * |in| is not changed. It returns one on success (i.e. |*ber_found| was set) * and zero on error. */ static int cbs_find_ber(CBS *orig_in, char *ber_found, unsigned depth) { CBS in; if (depth > kMaxDepth) return 0; CBS_init(&in, CBS_data(orig_in), CBS_len(orig_in)); *ber_found = 0; while (CBS_len(&in) > 0) { CBS contents; unsigned tag; size_t header_len; if (!CBS_get_any_asn1_element(&in, &contents, &tag, &header_len)) return 0; if (CBS_len(&contents) == header_len && header_len > 0 && CBS_data(&contents)[header_len-1] == 0x80) { *ber_found = 1; return 1; } if (tag & CBS_ASN1_CONSTRUCTED) { if (!CBS_skip(&contents, header_len) || !cbs_find_ber(&contents, ber_found, depth + 1)) return 0; } } return 1; } /* * is_primitive_type returns true if |tag| likely a primitive type. Normally * one can just test the "constructed" bit in the tag but, in BER, even * primitive tags can have the constructed bit if they have indefinite * length. */ static char is_primitive_type(unsigned tag) { return (tag & 0xc0) == 0 && (tag & 0x1f) != (CBS_ASN1_SEQUENCE & 0x1f) && (tag & 0x1f) != (CBS_ASN1_SET & 0x1f); } /* * is_eoc returns true if |header_len| and |contents|, as returned by * |CBS_get_any_asn1_element|, indicate an "end of contents" (EOC) value. */ static char is_eoc(size_t header_len, CBS *contents) { return header_len == 2 && CBS_len(contents) == 2 && memcmp(CBS_data(contents), "\x00\x00", 2) == 0; } /* * cbs_convert_ber reads BER data from |in| and writes DER data to |out|. If * |squash_header| is set then the top-level of elements from |in| will not * have their headers written. This is used when concatenating the fragments of * an indefinite length, primitive value. If |looking_for_eoc| is set then any * EOC elements found will cause the function to return after consuming it. * It returns one on success and zero on error. */ static int cbs_convert_ber(CBS *in, CBB *out, char squash_header, char looking_for_eoc, unsigned depth) { if (depth > kMaxDepth) return 0; while (CBS_len(in) > 0) { CBS contents; unsigned tag; size_t header_len; CBB *out_contents, out_contents_storage; if (!CBS_get_any_asn1_element(in, &contents, &tag, &header_len)) return 0; out_contents = out; if (CBS_len(&contents) == header_len) { if (is_eoc(header_len, &contents)) return looking_for_eoc; if (header_len > 0 && CBS_data(&contents)[header_len - 1] == 0x80) { /* * This is an indefinite length element. If * it's a SEQUENCE or SET then we just need to * write the out the contents as normal, but * with a concrete length prefix. * * If it's a something else then the contents * will be a series of BER elements of the same * type which need to be concatenated. */ const char context_specific = (tag & 0xc0) == 0x80; char squash_child_headers = is_primitive_type(tag); /* * This is a hack, but it sufficies to handle * NSS's output. If we find an indefinite * length, context-specific tag with a definite, * primtive tag inside it, then we assume that * the context-specific tag is implicit and the * tags within are fragments of a primitive type * that need to be concatenated. */ if (context_specific && (tag & CBS_ASN1_CONSTRUCTED)) { CBS in_copy, inner_contents; unsigned inner_tag; size_t inner_header_len; CBS_init(&in_copy, CBS_data(in), CBS_len(in)); if (!CBS_get_any_asn1_element(&in_copy, &inner_contents, &inner_tag, &inner_header_len)) return 0; if (CBS_len(&inner_contents) > inner_header_len && is_primitive_type(inner_tag)) squash_child_headers = 1; } if (!squash_header) { unsigned out_tag = tag; if (squash_child_headers) out_tag &= ~CBS_ASN1_CONSTRUCTED; if (!CBB_add_asn1(out, &out_contents_storage, out_tag)) return 0; out_contents = &out_contents_storage; } if (!cbs_convert_ber(in, out_contents, squash_child_headers, 1 /* looking for eoc */, depth + 1)) return 0; if (out_contents != out && !CBB_flush(out)) return 0; continue; } } if (!squash_header) { if (!CBB_add_asn1(out, &out_contents_storage, tag)) return 0; out_contents = &out_contents_storage; } if (!CBS_skip(&contents, header_len)) return 0; if (tag & CBS_ASN1_CONSTRUCTED) { if (!cbs_convert_ber(&contents, out_contents, 0 /* don't squash header */, 0 /* not looking for eoc */, depth + 1)) return 0; } else { if (!CBB_add_bytes(out_contents, CBS_data(&contents), CBS_len(&contents))) return 0; } if (out_contents != out && !CBB_flush(out)) return 0; } return looking_for_eoc == 0; } int CBS_asn1_ber_to_der(CBS *in, uint8_t **out, size_t *out_len) { CBB cbb; /* * First, do a quick walk to find any indefinite-length elements. Most * of the time we hope that there aren't any and thus we can quickly * return. */ char conversion_needed; if (!cbs_find_ber(in, &conversion_needed, 0)) return 0; if (!conversion_needed) { *out = NULL; *out_len = 0; return 1; } CBB_init(&cbb, CBS_len(in)); if (!cbs_convert_ber(in, &cbb, 0, 0, 0)) { CBB_cleanup(&cbb); return 0; } return CBB_finish(&cbb, out, out_len); }