  A recent development in formal security protocol analysis is the Protocol
Composition Logic (PCL). We identify a number of problems with this logic as
well as with extensions of the logic, as defined in
[DDMP05,HSD+05,He05,Dat05,Der06,DDMR07]. The identified problems imply strong
restrictions on the scope of PCL, and imply that some currently claimed PCL
proofs cannot be proven within the logic, or make use of unsound axioms. Where
possible, we propose solutions for these problems.
