secp256k1_ec_privkey_negate and invalid privkeys #488

1. 
   dcousens commented at 6:15 am on November 29, 2017: contributor

   For keys greater than the order, secp256k1_scalar_negate returns strange results (understandable!).

   But, as a result, secp256k1_ec_privkey_negate, when called with an invalid private key, returns 1 (OK), and a ?private key?.

   Tripped me up for a bit when generating some test fixtures for secp256k1_ec_privkey_negate.

    00000000000000000000000000000000000000000000000000000000000000000 becomes 0000000000000000000000000000000000000000000000000000000000000000
    1ff00000000000000000000000000000000000000000000000000000000000000 becomes 00fffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141
    2ffff000000000000000000000000000000000000000000000000000000000000 becomes 0000fffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141
    3ffffff0000000000000000000000000000000000000000000000000000000000 becomes 000000fffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141
    4ffffffff00000000000000000000000000000000000000000000000000000000 becomes 00000000fffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141
    5ffffffffff000000000000000000000000000000000000000000000000000000 becomes 0000000000fffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141
    6ffffffffffff0000000000000000000000000000000000000000000000000000 becomes 000000000000fffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141
    7ffffffffffffff00000000000000000000000000000000000000000000000000 becomes 00000000000000fffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141
    8ffffffffffffffff000000000000000000000000000000000000000000000000 becomes 0000000000000000fffffffffffffffebaaedce6af48a03bbfd25e8cd0364141
    9ffffffffffffffffff0000000000000000000000000000000000000000000000 becomes 000000000000000000fffffffffffffebaaedce6af48a03bbfd25e8cd0364141
   10ffffffffffffffffffff00000000000000000000000000000000000000000000 becomes 00000000000000000000fffffffffffebaaedce6af48a03bbfd25e8cd0364141
   11ffffffffffffffffffffff000000000000000000000000000000000000000000 becomes 0000000000000000000000fffffffffebaaedce6af48a03bbfd25e8cd0364141
   12ffffffffffffffffffffffff0000000000000000000000000000000000000000 becomes 000000000000000000000000fffffffebaaedce6af48a03bbfd25e8cd0364141
   13ffffffffffffffffffffffffff00000000000000000000000000000000000000 becomes 00000000000000000000000000fffffebaaedce6af48a03bbfd25e8cd0364141
   14ffffffffffffffffffffffffffff000000000000000000000000000000000000 becomes 0000000000000000000000000000fffebaaedce6af48a03bbfd25e8cd0364141
   15ffffffffffffffffffffffffffffff0000000000000000000000000000000000 becomes 000000000000000000000000000000febaaedce6af48a03bbfd25e8cd0364141
   16ffffffffffffffffffffffffffffffff00000000000000000000000000000000 becomes fffffffffffffffffffffffffffffffe755db9cd5e9140777fa4bd19a06c8282
   17ffffffffffffffffffffffffffffffffff000000000000000000000000000000 becomes fffffffffffffffffffffffffffffffd765db9cd5e9140777fa4bd19a06c8282
   18ffffffffffffffffffffffffffffffffffff0000000000000000000000000000 becomes fffffffffffffffffffffffffffffffd755eb9cd5e9140777fa4bd19a06c8282
   19ffffffffffffffffffffffffffffffffffffff00000000000000000000000000 becomes fffffffffffffffffffffffffffffffd755dbacd5e9140777fa4bd19a06c8282
   20ffffffffffffffffffffffffffffffffffffffff000000000000000000000000 becomes fffffffffffffffffffffffffffffffd755db9ce5e9140777fa4bd19a06c8282
   21ffffffffffffffffffffffffffffffffffffffffff0000000000000000000000 becomes fffffffffffffffffffffffffffffffd755db9cd5f9140777fa4bd19a06c8282
   22ffffffffffffffffffffffffffffffffffffffffffff00000000000000000000 becomes fffffffffffffffffffffffffffffffd755db9cd5e9240777fa4bd19a06c8282
   23ffffffffffffffffffffffffffffffffffffffffffffff000000000000000000 becomes fffffffffffffffffffffffffffffffd755db9cd5e9141777fa4bd19a06c8282
   24ffffffffffffffffffffffffffffffffffffffffffffffff0000000000000000 becomes fffffffffffffffffffffffffffffffd755db9cd5e9140787fa4bd19a06c8282
   25ffffffffffffffffffffffffffffffffffffffffffffffffff00000000000000 becomes fffffffffffffffffffffffffffffffd755db9cd5e91407780a4bd19a06c8282
   26ffffffffffffffffffffffffffffffffffffffffffffffffffff000000000000 becomes fffffffffffffffffffffffffffffffd755db9cd5e9140777fa5bd19a06c8282
   27ffffffffffffffffffffffffffffffffffffffffffffffffffffff0000000000 becomes fffffffffffffffffffffffffffffffd755db9cd5e9140777fa4be19a06c8282
   28ffffffffffffffffffffffffffffffffffffffffffffffffffffffff00000000 becomes fffffffffffffffffffffffffffffffd755db9cd5e9140777fa4bd1aa06c8282
   29ffffffffffffffffffffffffffffffffffffffffffffffffffffffffff000000 becomes fffffffffffffffffffffffffffffffd755db9cd5e9140777fa4bd19a16c8282
   30ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff0000 becomes fffffffffffffffffffffffffffffffd755db9cd5e9140777fa4bd19a06d8282
   31ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff00 becomes fffffffffffffffffffffffffffffffd755db9cd5e9140777fa4bd19a06c8382
   

2. 
   dcousens commented at 6:15 am on September 24, 2018: contributor

   Is this a bug or? Do I close?
3. 
   apoelstra commented at 10:44 pm on September 26, 2018: contributor

   I think it’s a documentation bug. We should state clearly that secp256k1_ec_privkey_negate will work only on valid secret keys, and that mysterious things will happen otherwise.
4. jonasnick cross-referenced this on Oct 7, 2019 from issue Return 0 if invalid seckey is given to ec_privkey_negate by jonasnick
5. jonasnick cross-referenced this on Oct 9, 2019 from issue Make ec_ arithmetic more consistent and add documentation by jonasnick
6. real-or-random closed this on Apr 30, 2020

   ---

Contributors
dcousens apoelstra