Not sure what's your use-case and threat model, but HKDF is likely what you want, the concatenation is done in a way to prevent attacks: https://www.rfc-editor

Not sure what's your use-case and threat model, but HKDF is likely what you want, the concatenation is done in a way to prevent attacks: https://www.rfc-editor.org/rfc/rfc5869 https://www.rfc-editor.org/rfc/rfc5869