How To: Sign Data Using Multisig

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ed25519verify indeed can only verify standard ED25519 signatures, not multisig ones.

However, you should be able to simulate a multisig using TEAL script. Here is a draft for a 2-out-of-3 multisig (where public keys are pk1, pk2, pk3) (disclaimer: I’ve not tested the following TEAL script nor reviewed the security):

arg_0 // data
arg_1 // signature under pk1 or empty
addr PK1 // load pk1
ed25519verify

arg_0 // data
arg_2 // signature under pk2 or empty
addr PK2 // load pk2
ed25519verify

arg_0 // data
arg_3 // signature under pk3 or empty
addr PK3 // load pk3
ed25519verify

// at this point on the stack, there should be 3 integers
// 0/1 for each potential signature
+
+ // compute the number of ed25519verify that passed
int 2
>= // check that it's above the threshold = 2

If you know how to sign under pk2 and pk3, you generate these signatures s2 and s3, and call the TEAL script with the following 4 arguments: data, empty, s2, s3.

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