Before this commit secp256k1_context_randomize called illegal_callback
when called on a context not initialized for signing. This is not
documented. Moreover, it is not desirable because non-signing contexts
may use randomization in the future.
This commit makes secp256k1_context_randomize a noop in this case. This
is safe because the context cannot be used for signing anyway.
This fixes#573 and it fixesrust-bitcoin/rust-secp256k1#82.
Identifiers starting with an underscore and followed immediately by a capital letter are reserved by the C++ standard.
The only header guards not fixed are those in the headers auto-generated from java.
bc61b91 add pubkey prefix constants to include/secp256k1.h (Andrew Poelstra)
Pull request description:
In future multisig implementations we will need to pass nonces around, which are algebraically pubkeys but should not be decodable as pubkeys. The way to do this is to change the prefix byte from the ordinary 0x02/0x03 to something else. However, some forks (notably `secp256k1-zkp`) have started using some bytes for their own encodings, and if we continue to use hardcoded constants the risk of conflict is increased.
This commit puts the prefixes used by the main library into the `include/secp256k1.h` so that the constants we're using will at least be in a standard easy-to-reference place.
Tree-SHA512: 37fa25be5074b7c519a9c69421320a62f32a3818f144254eb57f96c6657b993fc01962a5c670574275d1c59b095a6c89e60736123f032d6736907284eac526d7
I think I summarized it correctly after IRC discussion with gmaxwell
and andytoshi; I didn't know it existed :(
It's regrettable to expose this level of detail, but users need to know
this to make a decision about how to use it.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
These functions are intended for compatibility with legacy software,
and are not normally needed in new secp256k1 applications.
They also do not obeying any particular standard (and likely cannot
without without undermining their compatibility), and so are a
better fit for contrib.
ECDSA signature verification now requires normalized signatures (with S in the
lower half of the range). In case the input cannot be guaranteed to provide this,
a new function secp256k1_ecdsa_signature_normalize is provided to preprocess it.
There are now 2 encoding formats supported: 64-byte "compact" and DER.
The latter is strict: the data has to be exact DER, though the values
inside don't need to be valid.
The use of static makes this somewhat redundant currently, though if
we later have multiple compilation units it will be needed.
This also sets the dllexport needed for shared libraries on win32.
Right now `secp256k1_ec_pubkey_decompress` takes an in/out pointer to
a public key and replaces the input key with its decompressed variant.
This forces users who store compressed keys in small (<65 byte) fixed
size buffers (for example, the Rust bindings do this) to explicitly
and wastefully copy their key to a larger buffer.
[API BREAK]
This computes (n-b)G + bG with random value b, in place of nG in
ecmult_gen() for signing.
This is intended to reduce exposure to potential power/EMI sidechannels
during signing and pubkey generation by blinding the secret value with
another value which is hopefully unknown to the attacker.
It may not be very helpful if the attacker is able to observe the setup
or if even the scalar addition has an unacceptable leak, but it has low
overhead in any case and the security should be purely additive on top
of the existing defenses against sidechannels.
Tim Ruffing
Andrew Poelstra
Thomas Kerin
Dan Raviv
Pieter Wuille
Rusty Russell
Gregory Maxwell
Luke Dashjr
Thomas Kerin
Daniel Cousens