Following is a list of documents originally on www.invisiblenet.net/i2p/ and rescued via the Wayback Machine. They are quite dated and may or may not be accurate. However, the I2CP and I2NP documents in particular have some good information.
Index of /i2p
Name Last modified Size
I2CP_spec.pdf 03-Sep-2003 12:49 119k I2NP_spec.pdf 03-Sep-2003 12:49 356k datastructures.pdf 03-Sep-2003 12:49 149k i2p_philosophy.pdf 03-Sep-2003 12:52 126k polling_http_transpo..> 03-Sep-2003 12:49 189k