# validate_signer · FT4 Rell API · Chromia Docs (concept)

> function validate_ signer(signer: byte_ array) Checks if the signer has the correct size Throws "UNSUPPORTED SIGNER" if the signer's size does not match ei

Source: https://docs.chromia.com/pages/ft4-rell/-f-t4-library/lib.ft4.core.auth/validate_signer/

FUNCTION

# validate\_signer

```signature
function validate_signer(signer: byte_array)
```

[Source](https://gitlab.com/chromaway/ft4-lib/-/blob/development/rell/src/lib/ft4/core/auth/authentication.rell#lines-686)

Checks if the signer has the correct size

Throws `"UNSUPPORTED SIGNER"` if the signer's size does not match either:

* `EVM_ADDRESS_SIZE` length of 20 bytes
* `FT_PUBKEY_SIZE` length of 33 bytes

Should be used to validate the signer's size of an evm address or an ft pubkey

Example: `validate_signer(x"")`
will throw this error: UNSUPPORTED SIGNER: Unsupported signer x""

[View this page on docs.chromia.com](https://docs.chromia.com/pages/ft4-rell/-f-t4%20-library/lib.ft4.core.auth/validate_signer.html)Generated API reference, mirrored from the live docs