(PECL rnp >= 0.1.1)
rnp_op_sign_cleartext — Perform signing operation on a textual data, return cleartext signed message
ffiThe FFI object returned by rnp_ffi_create.
dataData to be signed.
keys_fp
      Array with key fingerprints. At least one key must be provided.
      Keys should be present in ffi.
     
optionsAn associative array with options.
| Key | Data type | 说明 | 
|---|---|---|
"armor" | 
         boolean | Enable ASCII-armored output. Disabled by default. | 
"hash" | 
         string | Set hash algorithm used during signature calculation. | 
"creation_time" | 
         integer | Set signature creation time in seconds since Jan, 1 1970 UTC. By default current time is used. | 
"expiration_time" | 
         integer | Set signature expiration time in seconds since the creation time. 0 value is used to mark signature as non-expiring (default value). | 
   Cleartext signed message containing source data with
   additional headers and ASCII-armored signature on success 或者在失败时返回 false.