libolm-dev 3.1.3+dfsg-2build2 (armhf binary) in ubuntu focal

 Olm is an implementation of the Double Ratchet cryptographic ratchet described
 by https://whispersystems.org/docs/specifications/doubleratchet/, written in C
 and C++11 and exposed as a C API.
 .
 This library also includes an implementation of the Megolm cryptographic
 ratchet which is intended for encrypted messaging applications where there
 may be a large number of recipients of each message, thus precluding the use of
 peer-to-peer encryption systems such as Olm.
 .
 Megolm is the end-to-end encryption system for the Matrix communications
 protocol.
 .
 This package contains the development files for compiling programs that use
 olm.