yum update fails: public key not available

[Jim Christiansen]

I have a problem updating my FC3 box.  I'm getting an error:

.
.
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  Update: zlib.i386 0:1.2.1.2-3.fc3
  Update: zlib-devel.i386 0:1.2.1.2-3.fc3

Performing the following to resolve dependencies:
  Install: python-crypto.i386 0:2.0.1-1.fc3
Is this ok [y/N]: y
Downloading Packages:
warning: rpmts_HdrFromFdno: V3 DSA signature: NOKEY, key ID 1ac70ce6
public key not available for 
//var/cache/yum/extras/packages/python-crypto-2.0.1-1.fc3.i386.rpm

How do I figure our what is depending on python-crypto?  or-  How do I fix 
the public key problem for it??

Thanks,  Jim