Help with secp256k1_schnorrsig_verify in a simple C# test console importing a generated libsecp256k1.dll

[ScoobyDooWho]

I was hoping someone could help me with this last problem... I've converted the C example to a C# one, everything works great until the last secp256k1_schnorrsig_verify that just crashes the app. Everything seems to be compiled right with the DLL or it wouldn't even work with a secp256k1_schnorrsig_sign32 call. As one test, if I try to create with a secp256k1_context_create(SECP256K1_CONTEXT_BOTH); (sign and verify 1|2), it crashes right off the top. Not sure what I'm missing here.
Impl Notes:
Client Flow (Unity 3D client .Net 4.8, which is why I've gotta compile a 2,0 framework version):

Client requests challenge from server

Server returns a challenge (random message hash)

Client signs the challenge with private key using simple DLL I've compiled with the C secp256k1 DLL (This all works)

Client POSTs public key, signature, challenge, and session ID

Server verifies the signature: secp256k1_schnorrsig_verify ... This bombs... In the simple end to end C# console test, doesn't work.

If valid, login continues
Compile of DLL on Windows 11 x64 machine Using MSYS2 MinGW 64-bit

git clone https://github.com/bitcoin-core/secp256k1
./autogen.sh
./configure --enable-module-schnorrsig --enable-experimental
make

I appreciate any help!

Example_Program .txt

[real-or-random]

secp256k1_context_create(SECP256K1_CONTEXT_BOTH)

Have you seen the docs? Just use SECP256K1_CONTEXT_BOTH, all other flags are deprecated, see

secp256k1/include/secp256k1.h

Line 266 in 9fab425

* In: flags: Always set to SECP256K1_CONTEXT_NONE (see below).

               // Deserialize public key and verify signature
               byte[] parsedPubkey = new byte[32];
               if (secp256k1_xonly_pubkey_parse(ctx, parsedPubkey, serializedPubkey) == 0)

secp256k1_xonly_pubkey needs 64 bytes, not just 32 bytes, see https://github.com/bitcoin-core/secp256k1/blob/master/include/secp256k1_extrakeys.h#L22.

[ScoobyDooWho]

Thank you for the reply.

I've seen many things, including following along with the very example on the main Hub page. As I stated, the core problem is that the very opening call when using secp256k1_context_create(SECP256K1_CONTEXT_BOTH); <--- Fails with [libsecp256k1] illegal argument: Invalid flags .

If I just use SECP256K1_CONTEXT_SIGN, all of it works fine even with 32 Byte declaration size, until secp256k1_schnorrsig_verify .

[real-or-random]

• Sorry, I mistyped my previous message. I meant to say SECP256K1_CONTEXT_NONE. This is the only one which is not deprecated.
• Your definitions of the flags are wrong, see

  secp256k1/include/secp256k1.h

  Lines 190 to 206 in 9fab425

  	/* All flags' lower 8 bits indicate what they're for. Do not use directly. */
  	#define SECP256K1_FLAGS_TYPE_MASK ((1 << 8) - 1)
  	#define SECP256K1_FLAGS_TYPE_CONTEXT (1 << 0)
  	#define SECP256K1_FLAGS_TYPE_COMPRESSION (1 << 1)
  	/* The higher bits contain the actual data. Do not use directly. */
  	#define SECP256K1_FLAGS_BIT_CONTEXT_VERIFY (1 << 8)
  	#define SECP256K1_FLAGS_BIT_CONTEXT_SIGN (1 << 9)
  	#define SECP256K1_FLAGS_BIT_CONTEXT_DECLASSIFY (1 << 10)
  	#define SECP256K1_FLAGS_BIT_COMPRESSION (1 << 8)
  	/** Context flags to pass to secp256k1_context_create, secp256k1_context_preallocated_size, and
  	* secp256k1_context_preallocated_create. */
  	#define SECP256K1_CONTEXT_NONE (SECP256K1_FLAGS_TYPE_CONTEXT)
  	/** Deprecated context flags. These flags are treated equivalent to SECP256K1_CONTEXT_NONE. */
  	#define SECP256K1_CONTEXT_VERIFY (SECP256K1_FLAGS_TYPE_CONTEXT | SECP256K1_FLAGS_BIT_CONTEXT_VERIFY)
  	#define SECP256K1_CONTEXT_SIGN (SECP256K1_FLAGS_TYPE_CONTEXT | SECP256K1_FLAGS_BIT_CONTEXT_SIGN)

  for the right integer values.

If I just use SECP256K1_CONTEXT_SIGN, all of it works fine even with 32 Byte declaration size, until secp256k1_schnorrsig_verify .

That doesn't change the fact that 32 is wrong.

[ScoobyDooWho]

• Sorry, I mistyped my previous message. I meant to say SECP256K1_CONTEXT_NONE. This is the only one which is not deprecated.
• Your definitions of the flags are wrong, see

  secp256k1/include/secp256k1.h

  Lines 190 to 206 in 9fab425

  	/* All flags' lower 8 bits indicate what they're for. Do not use directly. */
  	#define SECP256K1_FLAGS_TYPE_MASK ((1 << 8) - 1)
  	#define SECP256K1_FLAGS_TYPE_CONTEXT (1 << 0)
  	#define SECP256K1_FLAGS_TYPE_COMPRESSION (1 << 1)
  	/* The higher bits contain the actual data. Do not use directly. */
  	#define SECP256K1_FLAGS_BIT_CONTEXT_VERIFY (1 << 8)
  	#define SECP256K1_FLAGS_BIT_CONTEXT_SIGN (1 << 9)
  	#define SECP256K1_FLAGS_BIT_CONTEXT_DECLASSIFY (1 << 10)
  	#define SECP256K1_FLAGS_BIT_COMPRESSION (1 << 8)
  	/** Context flags to pass to secp256k1_context_create, secp256k1_context_preallocated_size, and
  	* secp256k1_context_preallocated_create. */
  	#define SECP256K1_CONTEXT_NONE (SECP256K1_FLAGS_TYPE_CONTEXT)
  	/** Deprecated context flags. These flags are treated equivalent to SECP256K1_CONTEXT_NONE. */
  	#define SECP256K1_CONTEXT_VERIFY (SECP256K1_FLAGS_TYPE_CONTEXT | SECP256K1_FLAGS_BIT_CONTEXT_VERIFY)
  	#define SECP256K1_CONTEXT_SIGN (SECP256K1_FLAGS_TYPE_CONTEXT | SECP256K1_FLAGS_BIT_CONTEXT_SIGN)

  
  for the right integer values.

If I just use SECP256K1_CONTEXT_SIGN, all of it works fine even with 32 Byte declaration size, until secp256k1_schnorrsig_verify .

That doesn't change the fact that 32 is wrong.

Thanks for staying Real Random! :) . I got it all fixed up now. I had SECP256K1_FLAGS_TYPE_CONTEXT as SECP256K1_CONTEXT_SIGN ( 1<<0) for the define in my c# test bed, so I got that fixed up and as you are saying, SECP256K1_FLAGS_TYPE_CONTEXT is the only one. Same value but now the trail of understanding becomes more clear.

I switched secp256k1_keypair_xonly_pub to use 64 bytes and once I looked at the schnorr.c file in more detail, I realized my DLL import declaration for secp256k1_schnorrsig_verify was missing a param: public static extern int secp256k1_schnorrsig_verify(IntPtr ctx, byte[] sig64, byte[] msg, missing-->uint msg_len<-- , byte[] pubkey);

After fixing it up, I now have a full working test bed in C# that can be used in .Net 461 framework.

Thanks again for the help.

I've attached the small c# test file for anyone in the future that comes across this problem.

Secp256k1_C#_net461_WorkingExample.txt