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boringssl/crypto/dsa/internal.h

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Bound RSA and DSA key sizes better. Most asymmetric operations scale superlinearly, which makes them potential DoS vectors. This (and other problems) are mitigated with fixed sizes, like RSA-2048, P-256, or curve25519. In older algorithms like RSA and DSA, these sizes are conventions rather than well-defined algorithms. "Everyone" uses RSA-2048, but code which imports an RSA key may see an arbitrary key size, possibly from an untrusted source. This is commonly a public key, so we bound RSA key sizes in check_modulus_and_exponent_sizes. However, some applications import external private keys, and may need tighter bounds. These typically parse the key then check the result. However, parsing itself can perform superlinear work (RSA_check_key or recovering the DSA public key). This CL does the following: - Rename check_modulus_and_exponent_sizes to rsa_check_public_key and additionally call it from RSA_check_key. - Fix a bug where RSA_check_key, on CRT-less keys, did not bound d, and bound p and q before multiplying (quadratic). - Our DSA verifier had stricter checks on q (160-, 224-, and 256-bit only) than our DSA signer (multiple of 8 bits). Aligner the signer to the verifier's checks. - Validate DSA group sizes on parse, as well as priv_key < q, to bound the running time. Ideally these invariants would be checked exactly once at construction, but our RSA and DSA implementations suffer from some OpenSSL's API mistakes (https://crbug.com/boringssl/316), which means it is hard to consistently enforce invariants. This CL focuses on the parser, but later I'd like to better rationalize the freeze_private_key logic. Performance of parsing RSA and DSA keys, gathered on my laptop. Did 15130 RSA-2048 parse operations in 5022458us (3012.5 ops/sec) Did 4888 RSA-4096 parse operations in 5060606us (965.9 ops/sec) Did 354 RSA-16384 parse operations in 5043565us (70.2 ops/sec) Did 88 RSA-32768 parse operations in 5038293us (17.5 ops/sec) [rejected by this CL] Did 35000 DSA-1024/256 parse operations in 5030447us (6957.6 ops/sec) Did 11316 DSA-2048/256 parse operations in 5094664us (2221.1 ops/sec) Did 5488 DSA-3072/256 parse operations in 5096032us (1076.9 ops/sec) Did 3172 DSA-4096/256 parse operations in 5041220us (629.2 ops/sec) Did 840 DSA-8192/256 parse operations in 5070616us (165.7 ops/sec) Did 285 DSA-10000/256 parse operations in 5004033us (57.0 ops/sec) Did 74 DSA-20000/256 parse operations in 5066299us (14.6 ops/sec) [rejected by this CL] Update-Note: Some invalid or overly large RSA and DSA keys may previously have been accepted that are now rejected at parse time. For public keys, this only moves the error from verification to parsing. In some private key cases, we would previously allow signing with those keys, but the resulting signatures would not be accepted by BoringSSL anyway. This CL makes us behave more consistently. Bug: oss-fuzz:24730 Change-Id: I4ad2003ee61138b693e65d3da4c6aa00bc165251 Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/42504 Reviewed-by: Adam Langley <agl@google.com>
5 years ago
/* Copyright (c) 2020, 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. */
#ifndef OPENSSL_HEADER_DSA_INTERNAL_H
#define OPENSSL_HEADER_DSA_INTERNAL_H
#include <openssl/dsa.h>
#if defined(__cplusplus)
extern "C" {
#endif
// dsa_check_parameters checks that |dsa|'s group is within DoS bounds. It
// returns one on success and zero on error.
int dsa_check_parameters(const DSA *dsa);
#if defined(__cplusplus)
} // extern C
#endif
#endif // OPENSSL_HEADER_DSA_INTERNAL_H