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Document encryption / decryption of private messages
This commit is contained in:
June Rhodes
parent
455ff2fcfc
commit
43717e9a15
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@ -91,7 +91,7 @@ This block is expected to appear within a post. As an example within an Atom fe
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<pm:recipient>
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<pm:canonicalUri>https://mastodon.social/users/user1.atom</pm:canonicalUri>
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<pm:publicKeyUri>https://mastodon.social/users/user1.pem</pm:publicKeyUri>
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<pm:encryptedSymmetricKey encoding="utf-8">
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<pm:encryptedSymmetricKey format="aes-256-cbc">
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<!--
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the symmetric key used to encrypt the actual content would be encrypted with the user's public key, and then included here in a base-64 format
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-->
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@ -101,7 +101,7 @@ This block is expected to appear within a post. As an example within an Atom fe
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<pm:recipient>
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<pm:canonicalUri>https://mastodon.social/users/user2.atom</pm:canonicalUri>
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<pm:publicKeyUri>https://mastodon.social/users/user2.pem</pm:publicKeyUri>
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<pm:encryptedSymmetricKey encoding="utf-8">
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<pm:encryptedSymmetricKey format="aes-256-cbc">
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<!--
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the symmetric key used to encrypt the actual content would be encrypted with the user's public key, and then included here in a base-64 format
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-->
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@ -116,4 +116,132 @@ As a convention, the unencrypted fields `content` and `title` should be replaced
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content with anything. Implementors should ensure they do not add `<link>` tags (such as mentions) or any other data to the entry that reveals any part of the contents
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of the private message.
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** TODO** This is a work in progress.
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For example, let's say we wanted to encrypt the message "hello" for the user `user1`. `user1`'s public key is:
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```
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-----BEGIN PUBLIC KEY-----
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MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAyLzIfIMU6+Aeh/RK45kP
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liWw/QDOp6I7n9lDNdCQ4x0rzUGiw5TEc6hprssWbRq1zcY4j6vTSGYFIaWi0XMW
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woDN18+M7H8wrTlnyYCz2nP6lWT27vAUreGtWlRjE0IuxuWPlSfWhBY9de2uUazt
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wBmKZdendV33X43IgoXZa14Zj1WqQjJuoeQ8AWDRSKk1pcAGVOVmgaqPYIWHOU87
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6Qe1z3qGLTv5PwscibJhIFRJd2UO6plS4srkSRjlNk+Dsh4Ommw+Fxkc7Xveazao
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omhFQIDZKUAT+mBREquony6YighGgnHaot1+lCPD2bi33xhBu9uEXxk9nT3cWSsb
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swIDAQAB
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-----END PUBLIC KEY-----
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```
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Their private key, which only their instance would have a copy of:
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```
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-----BEGIN PRIVATE KEY-----
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MIIEvwIBADANBgkqhkiG9w0BAQEFAASCBKkwggSlAgEAAoIBAQDIvMh8gxTr4B6H
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9ErjmQ+WJbD9AM6nojuf2UM10JDjHSvNQaLDlMRzqGmuyxZtGrXNxjiPq9NIZgUh
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paLRcxbCgM3Xz4zsfzCtOWfJgLPac/qVZPbu8BSt4a1aVGMTQi7G5Y+VJ9aEFj11
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7a5RrO3AGYpl16d1XfdfjciChdlrXhmPVapCMm6h5DwBYNFIqTWlwAZU5WaBqo9g
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hYc5TzvpB7XPeoYtO/k/CxyJsmEgVEl3ZQ7qmVLiyuRJGOU2T4OyHg6abD4XGRzt
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e95rNqiiaEVAgNkpQBP6YFESq6ifLpiKCEaCcdqi3X6UI8PZuLffGEG724RfGT2d
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PdxZKxuzAgMBAAECggEATq5whx16HdqDHRcMI5njGh87+G9QkTRt2oH2bimKIPtW
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J+YKPk8ZkZv5kKHZ8Hn/uOBxWx8mecJDUKTz5NUPnr2N8YFQ44IXOk6996WS2ZWM
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KvKgN5ezA1Tp9fYNv4a5fwyL8xLianOtM4QuR6VYq2tXbAPTh5WFWNbiOQbt6b8O
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mMsDgtdwp/4s/K4g0zLa7cXF89+0PqwgJ+hBM1Fc8FNyYhcpV1g0CsviLNVO2II/
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VknbjMBaFv1K44tKaYP+H1AdJuFmsCeGaoDp+3wx3Ay7BKn86c4NIkSGcT9hyJUy
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FKdzMC4g1O15t+wtULeFc7cMzWlTr1rr4G/hb0JegQKBgQDvtDdkS8HCM64bH9qG
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+zwvFl7wDLuQgFYw2F0McNnkBUz+3k1r6HnxiRLB0R3CQGoCdH4yOsCsS1U+3pZe
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0jC4u5kRU102zv5D8meRdACAjAZdTNuEddMpaKNmkYOsKF7WVcyZH3HTx7oMRUKU
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L1dGquFezL+sHkZfu52ZP18vawKBgQDWYmWqMxUImW8+CD2Ge3iGWsDM/1E4Kfxx
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d2ldkVeaXTpUL6p6MZu6WMVwjwxpeuQ4QbbE3NpBvrDdItq447Kbu3XMBFeu2Z9d
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yLL9g8lbbbJHcxPlIGGbFFAA2ZgM970TgY1Rd2WWaXdU6klV9wdewUjR1AVFeJDm
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sozevAA+2QKBgQCrU4oL28HfhoS4ymms9MEtfrXYqaEeRTxVqS/IhpiWS9ueh1Gb
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AQy3wJtxgH/eqZ+bpZvVVv0DqMyDJSEhIObGAwACzCzh0c0Wz5mK8viw6GRcJ2T3
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JigJfsrbssIEOM6gL68O+tSm5ChsQMy3kaa10clHstyErxbpsfWQ5SSphQKBgQCF
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nKu6CL4qLt5q7d3Si+9Q5QzWdqWa+GfyG7cabrQHa+UnhNGd+H8TA7KB9VWKA+Jq
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wWH0jaSlZwB5wfhJVPgDITFIZshzHAS8AZK0d8ct6U88Qpd6rNTIPz+hV/vw0RIR
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LyPxSxWQScjqrl3oat44CwSkaZyjcIH2lf8/7jHE+QKBgQC7N5cV6UhN6Euc7PFr
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xKgxUyYtF4ViJ20AcqSfrASKH/Bazsyfgd60NtHr2KWXoWi2YRyKZkuQTTtbumOo
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NL2GLaMIwiq9tOrOZAqRsMGwSwx1hCiQ1+XjOPHenNopr2vPVPKzpnbKK3l3Uu3J
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lUlAl2j+bjcbJ9nqJckquVA6bw==
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-----END PRIVATE KEY-----
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```
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As the instance sending the private message, we would first generate a symmetric key for this post:
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```
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$ openssl rand -base64 32 > key.bin
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$ cat key.bin
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LVU+/YZASJnOUWvZkuk2fpeA0+OFwf6LMNInJkjTdUs=
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```
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Then we encrypt the symmetric key using the user's public key:
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```
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$ openssl rsautl -encrypt -inkey public_key.pem -pubin -in key.bin -out key.bin.enc
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$ cat key.bin.enc
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<encrypted binary data will be shown here>
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```
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Then we encrypt the post using the symmetric key that we know:
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```
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$ openssl enc -aes-256-cbc -salt -in plaintext.txt -out encrypted.bin -pass file:./key.bin
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$ cat encrypted.bin
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<encrypted binary data will be shown here>
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```
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Now we have our two encrypted pieces of content:
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* `encrypted.bin` - the message encrypted with the symmetric key
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* `key.bin.enc` - the symmetric key encrypted with `user1`'s public key
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Convert them to their base-64 representations:
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```
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$ base64 encrypted.bin
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U2FsdGVkX19GuBT+KBmtha4yYrWQGJDtgtcybT6r43I=
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$ base64 key.bin.enc
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Ca0Yp/wsc5yvwT7ZumNGoeuGi32FFR9VKTio0b+5neE3J1biU5yIhEvrJBeF+0/98dZSsBMqSte0
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MfKQGd3+u6Uk/OtfDFPmitdMIjUbKpbmAIwql9m7Xs47FboCu9cKMjO7ZHU7B9kiBrZPcKo9mK6C
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Xz1jvr1qQX5JRDNZ5gvCoA6kSjiEkj/8kNEdPFfbR4ZnD3mOYyRDizsNj3vkbLlIfnLiN2p2hIuK
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NV9BoqX6ZXgoqWtAe54iMxMsWCvbBACzS+ipWFDpEdXJYu3GzRwRqfRCVDHS2Ci0MbJb2MsdbfVc
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aiwJ2Owc926vXPAB2E0ctucafKpiAm5AaNYMKw==
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```
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Construct the `<private>` tag for the message appropriately:
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```xml
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<pm:private>
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<pm:encryptedContentBase64 encoding="utf-8">U2FsdGVkX19GuBT+KBmtha4yYrWQGJDtgtcybT6r43I=</pm:encryptedContentBase64>
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<pm:recipient>
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<pm:canonicalUri>https://mastodon.social/users/user1.atom</pm:canonicalUri>
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<pm:publicKeyUri>https://mastodon.social/users/user1.pem</pm:publicKeyUri>
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<pm:encryptedSymmetricKey format="aes-256-cbc">
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Ca0Yp/wsc5yvwT7ZumNGoeuGi32FFR9VKTio0b+5neE3J1biU5yIhEvrJBeF+0/98dZSsBMqSte0
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MfKQGd3+u6Uk/OtfDFPmitdMIjUbKpbmAIwql9m7Xs47FboCu9cKMjO7ZHU7B9kiBrZPcKo9mK6C
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Xz1jvr1qQX5JRDNZ5gvCoA6kSjiEkj/8kNEdPFfbR4ZnD3mOYyRDizsNj3vkbLlIfnLiN2p2hIuK
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NV9BoqX6ZXgoqWtAe54iMxMsWCvbBACzS+ipWFDpEdXJYu3GzRwRqfRCVDHS2Ci0MbJb2MsdbfVc
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aiwJ2Owc926vXPAB2E0ctucafKpiAm5AaNYMKw==
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</pm:encryptedSymmetricKey>
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</pm:recipient>
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</pm:private>
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```
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When an instance receives a post with a private element, and recognises the canonical URI of a recipient as residing
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on that instance, it attempts to decrypt the symmetric key using the private key of the user. As an example, this
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can be done with:
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```
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$ openssl rsautl -decrypt -inkey private_key.pem -in key.bin.enc -out key.bin
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$ cat key.bin
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LVU+/YZASJnOUWvZkuk2fpeA0+OFwf6LMNInJkjTdUs=
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```
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```
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$ openssl enc -d -aes-256-cbc -in encrypted.bin -out plaintext2.txt -pass file:./key.bin
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$ cat plaintext2.txt
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hello
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```
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@ -37,7 +37,7 @@
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<xs:complexType>
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<xs:simpleContent>
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<xs:extension base="xs:base64Binary">
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<xs:attribute name="encoding" type="xs:string" use="required" />
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<xs:attribute name="format" type="xs:string" use="required" />
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</xs:extension>
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</xs:simpleContent>
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</xs:complexType>
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