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--- nhscontactapp [2020/05/06 07:27] – [Does The contact app exchange values] mark
+++ nhscontactapp [2025/05/09 05:29] (current) – external edit 127.0.0.1
@@ Line 6: / Line 6: @@
 There are two main options, the first is a seed that is "spun" to generate the next value. Or a pure random value that is created each time. Both methods have there advantages and disadvantages, for example using a Seed means that the app only needs to store the seed and can calculate the values sent within a day easily, this means less storage is needed to store all the values, however leaking the seed allows an attacker to re-generate all the values the app generates for a given time.
+From https://www.ncsc.gov.uk/blog-post/security-behind-nhs-contact-tracing-app
+It looks like a seed is used.
+"Every day, your device generates a random elliptic curve key pair and encrypts your installation ID (and some other administrative stuff like time periods) with it in a way that only the NHS server can recover, "
 ===== How often is the Unique ID changed =====