From cd4f84f3ba8de37726274f61d5a34477c88433cf Mon Sep 17 00:00:00 2001 From: cheapshot003 Date: Thu, 29 Aug 2024 22:24:20 +0200 Subject: [PATCH] Improve examples/documentation: remove key generation loops Co-Authored by: Sebastian Falbesoner --- examples/ecdh.c | 22 ++++++++++------------ examples/ecdsa.c | 22 ++++++++++------------ examples/ellswift.c | 21 ++++++++++----------- examples/schnorr.c | 26 ++++++++++++-------------- include/secp256k1.h | 6 ++++-- 5 files changed, 46 insertions(+), 51 deletions(-) diff --git a/examples/ecdh.c b/examples/ecdh.c index d71fd2f604..ef9e8b896f 100644 --- a/examples/ecdh.c +++ b/examples/ecdh.c @@ -42,18 +42,16 @@ int main(void) { assert(return_val); /*** Key Generation ***/ - - /* If the secret key is zero or out of range (bigger than secp256k1's - * order), we try to sample a new key. Note that the probability of this - * happening is negligible. */ - while (1) { - if (!fill_random(seckey1, sizeof(seckey1)) || !fill_random(seckey2, sizeof(seckey2))) { - printf("Failed to generate randomness\n"); - return 1; - } - if (secp256k1_ec_seckey_verify(ctx, seckey1) && secp256k1_ec_seckey_verify(ctx, seckey2)) { - break; - } + if (!fill_random(seckey1, sizeof(seckey1)) || !fill_random(seckey2, sizeof(seckey2))) { + printf("Failed to generate randomness\n"); + return 1; + } + /* If the secret key is zero or out of range (greater than secp256k1's + * order), we fail. Note that the probability of this occurring + * is negligible with a properly functioning random number generator. */ + if (!secp256k1_ec_seckey_verify(ctx, seckey1) || !secp256k1_ec_seckey_verify(ctx, seckey2)) { + printf("Generated secret key is invalid. This indicates an issue with the random number generator.\n"); + return 1; } /* Public key creation using a valid context with a verified secret key should never fail */ diff --git a/examples/ecdsa.c b/examples/ecdsa.c index d5c4613d9c..433c58ffb8 100644 --- a/examples/ecdsa.c +++ b/examples/ecdsa.c @@ -49,18 +49,16 @@ int main(void) { assert(return_val); /*** Key Generation ***/ - - /* If the secret key is zero or out of range (bigger than secp256k1's - * order), we try to sample a new key. Note that the probability of this - * happening is negligible. */ - while (1) { - if (!fill_random(seckey, sizeof(seckey))) { - printf("Failed to generate randomness\n"); - return 1; - } - if (secp256k1_ec_seckey_verify(ctx, seckey)) { - break; - } + /* If the secret key is zero or out of range (greater than secp256k1's + * order), we return 1. Note that the probability of this occurring + * is negligible with a properly functioning random number generator. */ + if (!fill_random(seckey, sizeof(seckey))) { + printf("Failed to generate randomness\n"); + return 1; + } + if (!secp256k1_ec_seckey_verify(ctx, seckey)) { + printf("Generated secret key is invalid. This indicates an issue with the random number generator.\n"); + return 1; } /* Public key creation using a valid context with a verified secret key should never fail */ diff --git a/examples/ellswift.c b/examples/ellswift.c index 52be7eebfb..e6159f36c9 100644 --- a/examples/ellswift.c +++ b/examples/ellswift.c @@ -48,17 +48,16 @@ int main(void) { /*** Generate secret keys ***/ - /* If the secret key is zero or out of range (bigger than secp256k1's - * order), we try to sample a new key. Note that the probability of this - * happening is negligible. */ - while (1) { - if (!fill_random(seckey1, sizeof(seckey1)) || !fill_random(seckey2, sizeof(seckey2))) { - printf("Failed to generate randomness\n"); - return 1; - } - if (secp256k1_ec_seckey_verify(ctx, seckey1) && secp256k1_ec_seckey_verify(ctx, seckey2)) { - break; - } + /* If the secret key is zero or out of range (greater than secp256k1's + * order), we return 1. Note that the probability of this occurring + * is negligible with a properly functioning random number generator. */ + if (!fill_random(seckey1, sizeof(seckey1)) || !fill_random(seckey2, sizeof(seckey2))) { + printf("Failed to generate randomness\n"); + return 1; + } + if (!secp256k1_ec_seckey_verify(ctx, seckey1) || !secp256k1_ec_seckey_verify(ctx, seckey2)) { + printf("Generated secret key is invalid. This indicates an issue with the random number generator.\n"); + return 1; } /* Generate ElligatorSwift public keys. This should never fail with valid context and diff --git a/examples/schnorr.c b/examples/schnorr.c index 8d5d14bdaf..adced235b3 100644 --- a/examples/schnorr.c +++ b/examples/schnorr.c @@ -43,20 +43,18 @@ int main(void) { assert(return_val); /*** Key Generation ***/ - - /* If the secret key is zero or out of range (bigger than secp256k1's - * order), we try to sample a new key. Note that the probability of this - * happening is negligible. */ - while (1) { - if (!fill_random(seckey, sizeof(seckey))) { - printf("Failed to generate randomness\n"); - return 1; - } - /* Try to create a keypair with a valid context, it should only fail if - * the secret key is zero or out of range. */ - if (secp256k1_keypair_create(ctx, &keypair, seckey)) { - break; - } + /* If the secret key is zero or out of range (greater than secp256k1's + * order), we return 1. Note that the probability of this occurring + * is negligible with a properly functioning random number generator. */ + if (!fill_random(seckey, sizeof(seckey))) { + printf("Failed to generate randomness\n"); + return 1; + } + /* Try to create a keypair with a valid context, it should only fail if + * the secret key is zero or out of range. */ + if (!secp256k1_keypair_create(ctx, &keypair, seckey)) { + printf("Generated secret key is invalid. This indicates an issue with the random number generator.\n"); + return 1; } /* Extract the X-only public key from the keypair. We pass NULL for diff --git a/include/secp256k1.h b/include/secp256k1.h index cfbdd528c2..88928111c4 100644 --- a/include/secp256k1.h +++ b/include/secp256k1.h @@ -679,12 +679,14 @@ SECP256K1_API int secp256k1_ecdsa_sign( const void *ndata ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4); -/** Verify an ECDSA secret key. +/** Verify an elliptic curve secret key. * * A secret key is valid if it is not 0 and less than the secp256k1 curve order * when interpreted as an integer (most significant byte first). The * probability of choosing a 32-byte string uniformly at random which is an - * invalid secret key is negligible. + * invalid secret key is negligible. However, if it does happen it should + * be assumed that the randomness source is severely broken and there should + * be no retry. * * Returns: 1: secret key is valid * 0: secret key is invalid