Françoise Hardy sings Message personnel (music and lyrics Michel Berger). The spoken introduction was written by Françcoise Hardy and she also found the title, according to Wikipedia fr that also explains the genesis of the album.
Since I was looking up Charles Dumont, here is Ta cigarette après l'amour. He wrote the music and Sophie Makhno wrote the lyrics in 1968. This song helped him start a new career, different from the songs he had written for Piaf.