<html><body><div style="color:#000; background-color:#fff; font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:13px"><div dir="ltr" id="yui_3_16_0_1_1421628424408_4984"><span id="yui_3_16_0_1_1421628424408_4983">Re-encryption by clients is essential. Anything else does not preserve any of the useful security properties of PFS.</span></div><div dir="ltr" id="yui_3_16_0_1_1421628424408_4984"><span><br></span></div><div dir="ltr" id="yui_3_16_0_1_1421628424408_4984"><span id="yui_3_16_0_1_1421628424408_4996">In particular, if the sender and recipient store the same thing, it is later possible for an attacker to discover -- purely from the encrypted messages -- whether users have exchanged messages.</span></div><div dir="ltr" id="yui_3_16_0_1_1421628424408_4985"><span><br></span></div><div dir="ltr" id="yui_3_16_0_1_1421628424408_4986">Symmetric keys are short: it's feasible to use per-message keys in most situations. (And this it the simplest to implement thing.)</div><div></div><div id="yui_3_16_0_1_1421628424408_4992"> </div><div id="yui_3_16_0_1_1421628424408_4991"><div id="yui_3_16_0_1_1421628424408_4990">- dlg
<br></div></div> <div class="qtdSeparateBR"><br><br></div><div class="yahoo_quoted" style="display: block;"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 13px;"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;"> <div dir="ltr"> <font size="2" face="Arial"> On Sunday, January 18, 2015 3:51 PM, "steve@actor.im" <steve@actor.im> wrote:<br> </font> </div> <br><br> <div class="y_msg_container"><div id="yiv7091357048"><div><div>Re-encrypt and upload all messages? Seems to be weird for mobile world. And i don't understand how re-encrypting help to preserve PFS, we still has only one single long-term key for everything and it must be enough to decrypt messages.</div><div> </div><div>15.01.2015, 12:06, "Natanael" <natanael.l@gmail.com>:</div><div class="yiv7091357048yqt1193136715" id="yiv7091357048yqt32826"><blockquote type="cite"><div><br clear="none"> Den 15 jan 2015 03:47 skrev <<a rel="nofollow" shape="rect" ymailto="mailto:steve@actor.im" target="_blank" href="mailto:steve@actor.im">steve@actor.im</a>>:<br clear="none"> ><br clear="none"> > Hi everyone,<br clear="none"> ><br clear="none"> > Are there some best practices for keeping all encrypted message history securely on server or on client for accessing them later with single hardware or software key like ubikey?</div><div>To preserve PFS, let the client re-encrypt and upload. The client cloud sign or MAC the ciphertext to prevent modification.</div></blockquote></div><div> </div><div> </div><div>-- </div><div>Steve K,</div><div>CEO Actor.im</div><div> </div>
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