What doctrine holds that, w henever we knowingly reveal our incriminating secrets, we assume the risk that our false friends will use them against us in criminal cases?

Answer: Third party doctrine

Explanation: It is, in fact, a legal doctrine governing that if one voluntarily discloses his or her secrets, it is reasonable not to expect it to remain private. This may disclose information that should essentially be private, but when that information is disclosed to an ISP or bank or telephone company, then that third party may be able to access that information. So, if you opt for one of the mobile telephony packages, the number you bought from them may reach a third party, some company that will send you advertising messages, even though you have never personally given the company your information, the mobile operator has.

According to this doctrine, if you have disclosed your secrets to someone you believe to be a false friend, he / she will certainly pass that information on to someone, that is, in this particular case, it may be used against you.