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A bug in the implementation of the Tonelli-Shanks algorithm can lead to
an infinite loop. This loop can be hit in various ways, in particular on
decompressing an elliptic curve public key via EC_POINT_oct2point() - to
do this, one must solve y^2 = x^3 + ax + b for y, given x.
If a certificate uses explicit encoding for elliptic curve parameters,
this operation needs to be done during certificate verification, leading
to a DoS. In particular, everything dealing with untrusted certificates
is affected, notably TLS servers explicitly configured to request
client certificates (httpd, smtpd, various VPN implementations, ...).
Ordinary TLS servers do not consume untrusted certificates.
The problem is that we cannot assume that x^3 + ax + b is actually a
square on untrusted input and neither can we assume that the modulus
p is a prime. Ensuring that p is a prime is too expensive (it would
likely itself lead to a DoS). To avoid the infinite loop, fix the logic
to be more resilient and explicitly limit the number of iterations that
can be done. The bug is such that the infinite loop can also be hit for
primes = 3 (mod 4) but fortunately that case is optimized earlier.
It's also worth noting that there is a size bound on the field size
enforced via OPENSSL_ECC_MAX_FIELD_BITS (= 661), which help mitigate
further DoS vectors in presence of this fix.
Reported by Tavis Ormandy and David Benjamin, Google
Patch based on the fixes by David Benjamin and Tomas Mraz, OpenSSL
ok beck inoguchi
This is errata/6.9/032_bignum.patch.sig
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as was done earlier in libssl. Thanks inoguchi@ for noticing
libssl had more reacharounds into this.
ok jsing@ inoguchi@
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matter for constant time, and make the public interface only used
external to the library.
This moves us to a model where the important things are constant time
versions unless you ask for them not to be, rather than the opposite.
I'll continue with this method by method.
Add regress tests for same.
ok jsing@
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ok miod@
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There are currently cases where the return from each call is checked,
the return from only the last call is checked and cases where it is not
checked at all (including code in bn, ec and engine).
Checking the last return value is valid as once the function fails it will
continue to return NULL. However, in order to be consistent check each
call with the same idiom. This makes it easy to verify.
Note there are still a handful of cases that do not follow the idiom -
these will be handled separately.
ok beck@ doug@
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Remove the openssl public includes from cryptlib.h and add a small number
of includes into the source files that actually need them. While here,
also sort/group/tidy the includes.
ok beck@ miod@
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