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FairEmail
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Added native ARC verification

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pull/212/head
M66B 2 years ago
parent cb9102b9ed
commit 32945cc721
1 changed files with 88 additions and 0 deletions
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88
app/src/main/java/eu/faircode/email/MessageHelper.java
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@ -181,7 +181,15 @@ public class MessageHelper {
private static final int FORMAT_FLOWED_LINE_LENGTH = 72; // characters
private static final int MAX_DIAGNOSTIC = 250; // characters
private static final int DKIM_MIN_TEXT = 100; // characters
private static final String DKIM_SIGNATURE = "DKIM-Signature";
private static final String ARC_SEAL = "ARC-Seal";
private static final String ARC_AUTHENTICATION_RESULTS = "ARC-Authentication-Results";
private static final String ARC_MESSAGE_SIGNATURE = "ARC-Message-Signature";
static final List<String> ARC_WHITELIST = Collections.unmodifiableList(Arrays.asList(
"google.com", "microsoft.com"
));
private static final String DOCTYPE = "<!DOCTYPE";
private static final String HTML_START = "<html>";
@ -2019,6 +2027,86 @@ public class MessageHelper {
}
Log.i("DKIM signers=" + TextUtils.join(",", signers));
if (signers.size() == 0) {
// https://datatracker.ietf.org/doc/html/rfc8617#section-5.2
boolean ok = true; // Until it is not
Map<Integer, String> as = new HashMap<>();
Map<Integer, String> aar = new HashMap<>();
Map<Integer, String> ams = new HashMap<>();
// 1. Collect all ARC Sets currently attached to the message
for (String n : new String[]{ARC_SEAL, ARC_AUTHENTICATION_RESULTS, ARC_MESSAGE_SIGNATURE}) {
Map<Integer, String> map;
if (ARC_SEAL.equals(n))
map = as;
else if (ARC_AUTHENTICATION_RESULTS.equals(n))
map = aar;
else if (ARC_MESSAGE_SIGNATURE.equals(n))
map = ams;
else
throw new IllegalArgumentException(n);
headers = amessage.getHeader(n);
if (headers != null) {
for (String header : headers) {
Map<String, String> kv = getKeyValues(MimeUtility.unfold(header));
Integer i = Helper.parseInt(kv.get("i"));
if (i == null || map.containsKey(i)) {
// 3.A. Each ARC Set MUST contain exactly one each of the three ARC header fields
Log.i("ARC duplicate " + n + "@" + i);
ok = false;
break;
}
map.put(i, header);
}
}
if (!ok)
break;
}
Log.i("ARC as=" + as.size() + " aar=" + aar.size() + " ams=" + ams.size() + " ok=" + ok);
if (ok &&
as.size() <= 50 &&
as.size() == aar.size() &&
as.size() == ams.size()) {
for (int i = 1; i <= as.size(); i++) {
// 3.B. The instance values of the ARC Sets MUST form a continuous sequence from 1..N with no gaps or repetition
if (!as.containsKey(i) || !aar.containsKey(i) || !ams.containsKey(i)) {
ok = false;
break;
}
// 2. If the Chain Validation Status of the highest instance value ARC Set is "fail",
// then the Chain Validation Status is "fail"
// 3.C. The "cv" value for all ARC-Seal header fields MUST NOT be "fail".
// For ARC Sets with instance values > 1, the values MUST be "pass".
// For the ARC Set with instance value = 1, the value MUST be "none".
Map<String, String> kv = getKeyValues(MimeUtility.unfold(as.get(i)));
String cv = kv.get("cv");
if (!(i == 1 ? "none" : "pass").equalsIgnoreCase(cv)) {
Log.i("ARC cv#" + i + "=" + cv);
ok = false;
break;
}
}
}
Log.i("ARC sets=" + ok);
// 4. Validate the AMS with the greatest instance value (most recent).
// If validation fails, then the Chain Validation Status is "fail", and the algorithm stops here.
if (ok) {
String arc = ams.get(ams.size());
String signer = verifySignatureHeader(context, arc, ARC_MESSAGE_SIGNATURE, amessage);
if (signer != null && !signers.contains(signer)) {
boolean whitelisted = ARC_WHITELIST.contains(signer);
Log.i("ARC signer=" + signer + " whitelisted=" + whitelisted);
if (whitelisted)
signers.add(signer);
}
}
}
} catch (Throwable ex) {
Log.e("DKIM", ex);
}

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