diff options
Diffstat (limited to 'crypto/bytestring/ber.c')
| -rw-r--r-- | crypto/bytestring/ber.c | 215 |
1 files changed, 215 insertions, 0 deletions
diff --git a/crypto/bytestring/ber.c b/crypto/bytestring/ber.c new file mode 100644 index 0000000..c96c200 --- /dev/null +++ b/crypto/bytestring/ber.c @@ -0,0 +1,215 @@ +/* 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 <openssl/bytestring.h> + +#include "internal.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, contents; + unsigned tag; + size_t header_len; + + CBS_init(&in_copy, CBS_data(in), CBS_len(in)); + if (!CBS_get_any_asn1_element(&in_copy, &contents, &tag, &header_len)) { + return 0; + } + if (CBS_len(&contents) > header_len && is_primitive_type(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); +} |