Rename msg32 to msghash32 in ecdsa_sign/verify and add explanation

[secp256k1.git] / README.md

diff --git a/README.md b/README.md
index e7eebe294fa8f6b5d1043c3bf775ee040d4f1994..e070937235c36a3f62f39c729d17e9abdc162a78 100644 (file)
--- a/README.md
+++ b/README.md
@@ -3,17 +3,22 @@ libsecp256k1
 
 [![Build Status](https://travis-ci.org/bitcoin-core/secp256k1.svg?branch=master)](https://travis-ci.org/bitcoin-core/secp256k1)
 
-Optimized C library for EC operations on curve secp256k1.
+Optimized C library for ECDSA signatures and secret/public key operations on curve secp256k1.
 
-This library is a work in progress and is being used to research best practices. Use at your own risk.
+This library is intended to be the highest quality publicly available library for cryptography on the secp256k1 curve. However, the primary focus of its development has been for usage in the Bitcoin system and usage unlike Bitcoin's may be less well tested, verified, or suffer from a less well thought out interface. Correct usage requires some care and consideration that the library is fit for your application's purpose.
 
 Features:
 * secp256k1 ECDSA signing/verification and key generation.
-* Adding/multiplying private/public keys.
-* Serialization/parsing of private keys, public keys, signatures.
-* Constant time, constant memory access signing and pubkey generation.
-* Derandomized DSA (via RFC6979 or with a caller provided function.)
+* Additive and multiplicative tweaking of secret/public keys.
+* Serialization/parsing of secret keys, public keys, signatures.
+* Constant time, constant memory access signing and public key generation.
+* Derandomized ECDSA (via RFC6979 or with a caller provided function.)
 * Very efficient implementation.
+* Suitable for embedded systems.
+* Optional module for public key recovery.
+* Optional module for ECDH key exchange.
+
+Experimental features have not received enough scrutiny to satisfy the standard of quality of this library but are made available for testing and review by the community. The APIs of these features should not be considered stable.
 
 Implementation details
 ----------------------
@@ -28,7 +33,7 @@ Implementation details
 * Field operations
   * Optimized implementation of arithmetic modulo the curve's field size (2^256 - 0x1000003D1).
     * Using 5 52-bit limbs (including hand-optimized assembly for x86_64, by Diederik Huys).
-    * Using 10 26-bit limbs.
+    * Using 10 26-bit limbs (including hand-optimized assembly for 32-bit ARM, by Wladimir J. van der Laan).
   * Field inverses and square roots using a sliding window over blocks of 1s (by Peter Dettman).
 * Scalar operations
   * Optimized implementation without data-dependent branches of arithmetic modulo the curve's order.
@@ -43,14 +48,14 @@ Implementation details
   * Use wNAF notation for point multiplicands.
   * Use a much larger window for multiples of G, using precomputed multiples.
   * Use Shamir's trick to do the multiplication with the public key and the generator simultaneously.
-  * Optionally (off by default) use secp256k1's efficiently-computable endomorphism to split the P multiplicand into 2 half-sized ones.
+  * Use secp256k1's efficiently-computable endomorphism to split the P multiplicand into 2 half-sized ones.
 * Point multiplication for signing
   * Use a precomputed table of multiples of powers of 16 multiplied with the generator, so general multiplication becomes a series of additions.
   * Intended to be completely free of timing sidechannels for secret-key operations (on reasonable hardware/toolchains)
     * Access the table with branch-free conditional moves so memory access is uniform.
     * No data-dependent branches
   * Optional runtime blinding which attempts to frustrate differential power analysis.
-  * The precomputed tables add and eventually subtract points for which no known scalar (private key) is known, preventing even an attacker with control over the private key used to control the data internally.
+  * The precomputed tables add and eventually subtract points for which no known scalar (secret key) is known, preventing even an attacker with control over the secret key used to control the data internally.
 
 Build steps
 -----------
@@ -72,6 +77,27 @@ With valgrind, you might need to increase the max stack size:
 
     $ valgrind --max-stackframe=2500000 ./exhaustive_tests
 
+Test coverage
+-----------
+
+This library aims to have full coverage of the reachable lines and branches.
+
+To create a test coverage report, configure with `--enable-coverage` (use of GCC is necessary):
+
+    $ ./configure --enable-coverage
+
+Run the tests:
+
+    $ make check
+
+To create a report, `gcovr` is recommended, as it includes branch coverage reporting:
+
+    $ gcovr --exclude 'src/bench*' --print-summary
+
+To create a HTML report with coloured and annotated source code:
+
+    $ gcovr --exclude 'src/bench*' --html --html-details -o coverage.html
+
 Reporting a vulnerability
 ------------