Man pages matching name rsa_sign_asn1_octet_string in section 3ssl:

RSA_sign_ASN1_OCTET_STRING.3ssl.en	debian 10 / libssl-doc
RSA_sign_ASN1_OCTET_STRING.3ssl.en	debian 11 / libssl-doc
RSA_sign_ASN1_OCTET_STRING.3ssl.en	debian 12 / libssl-doc