I am unable to get TCPDUMP to decrypt VPN packets for troubleshooting purposes. I manage both ends of the tunnel and have all required information (SPI, remote peer ip, enc, and key). I am not completely certain I understand the syntax.

I have tried several combinations including the following:
-E "spi@1.2.3.4 3des-cbc:12345"

If above is correct, please please answer the following questions:
1. SPI-is this hex or ascii?
2. Where can I get a list of supported encryptions and their syntax? The MAN page is incomplete. Ive seen 3DES written like DES3, 3DES-cbc, 3DES, DES3-CBC.
3. Preshare-Is this ascii or hex?
4. Are the quotes required

If the above syntax is incorrect, I would greatly appreciate the corrected syntax.

Thanks in advance for your assistance.