When an assembly is signed, a hash is taken from its relevant parts and encrypted with a private key. The encrypted hash and the public key are then stored within the assembly. The assembly thus becomes a strong named assembly.
A signed assembly can then be referenced from another assembly or exe, either at compile time (csc … /reference:assmbly.dll) or at run time (Assembly.Load(… public_key_token)).
A strong named assembly can only reference other strong named assemblies because otherwise they'd become insecure.
Display public key and public key token of signed assembly
The public key and public key token of a signed assembly can be shown with the sn.exe command line tool:
PS P:\rojects\xyz> sn -Tp .\tq84_asmb.dll
…
Public key (hash algorithm: sha1):
0024000004800000940000000602000000240000525341310004000001000100ed039243282431
4878e77c50dfae27cfc940ada2682700590334af38485a0644c65775b6ee7a8b8d532486d59017
6d3d9f84cde5eafd5547f0067dbc09ef3ae3add1f3d3cca52b4f851fdf386c6bab06f4e858619a
5e15491f04d82e379c778af321aee86aac3ebf74bc18584f03b5e34935c9ed3c99d16660a8d0b0
2a7725a9
Public key token is 203fb045f5c12ec9