What is cursing? Cursing is the calling down of some evil on a person, place, or thing.
Bless those who persecute you; bless and do not curse. (Romans 12:14)
What is blasphemy? Blasphemy is insulting language which expresses contempt for God, either directly or through His saints and holy things.
Amen I say to you, that all sins shall be forgiven to the sons of men, and the blasphemies wherewith they may blaspheme; but whoever blasphemes against the Holy Ghost never has forgiveness, but will be guilty of an everlasting sin. (Mark 3:28-30)
Further reading: CCC 2148