1ff9e92948 key: use static context for libsecp256k1 calls where applicable (Sebastian Falbesoner)
Pull request description:
The dynamically created [signing context](2d6a0c4649/src/key.cpp (L19)) for libsecp256k1 calls is only needed for functions that involve generator point multiplication with a secret key, i.e. different variants of public key creation and signing. The API docs hint to those by stating "[(not secp256k1_context_static)](b475654302/include/secp256k1.h (L645))" for the context parameter. In our case that applies to the following calls:
- `secp256k1_ec_pubkey_create`
- `secp256k1_keypair_create`
- `secp256k1_ellswift_create`
- `secp256k1_ecdsa_sign`
- `secp256k1_ecdsa_sign_recoverable`
- `secp256k1_schnorrsig_sign32`
- `ec_seckey_export_der` (not a direct secp256k1 function, but calls `secp256k1_ec_pubkey_create` inside)
For all the other secp256k1 calls we can simply use the static context. This is done for consistency to other calls that already use `secp256k1_context_static`, and also to reduce dependencies on the global signing context variable. Looked closer at this in the course of reviewing #29675, where some functions used the signing context that didn't need to, avoiding a move to another module (see https://github.com/bitcoin/bitcoin/pull/29675#discussion_r2333831377).
ACKs for top commit:
Eunovo:
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furszy:
ACK 1ff9e92948
rkrux:
crACK 1ff9e92948
Tree-SHA512: f091efa56c358057828f3455d4ca9ce40ec0d35f3e38ab147fe3928bb5dbf7ffbc27dbf97b71937828ab95ea4e9be5f96d89a2d29e2aa18df4542aae1b33e258
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