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Decrypt messages whose content key is wrapped with RSAES-OAEP - #635
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BCCryptoHelper.decrypt unwrapped the content key with BouncyCastle's lightweight BcRSAKeyTransEnvelopedRecipient, whose BcRSAAsymmetricKeyUnwrapper always uses PKCS#1 v1.5 and ignores the key-encryption algorithm named in the envelope. A key wrapped with RSAES-OAEP (1.2.840.113549.1.1.7) therefore failed with "unable to recover secret key: block incorrect", and the partner got a decryption-failed MDN. Microsoft BizTalk wraps with OAEP, so no message from a BizTalk partner could be received. JceKeyTransEnvelopedRecipient reads the algorithm from the recipient info and handles PKCS#1 v1.5 and OAEP alike. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Oct 25, 2026
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🚀 Thanks for the fix.
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Problem
An inbound message whose content key is wrapped with RSAES-OAEP (
1.2.840.113549.1.1.7) can't be decrypted. It fails with:The partner then gets a
processed/error:decryption-failedMDN. We hit this with a trading partner running Microsoft BizTalk, which wraps with OAEP. A packet capture confirmed the envelope was addressed to the correct certificate. Every message from that partner failed, while messages wrapped with PKCS#1 v1.5 decrypted fine.Cause
BCCryptoHelper.decryptunwraps with BouncyCastle's lightweightBcRSAKeyTransEnvelopedRecipient. Its unwrapper,BcRSAAsymmetricKeyUnwrapper.createAsymmetricUnwrapper, always returnsnew PKCS1Encoding(new RSABlindedEngine())and ignores the key-encryption algorithm named in the recipient info. So an OAEP-wrapped key is decoded as PKCS#1 v1.5 and fails the padding check.Fix
Use
JceKeyTransEnvelopedRecipient((PrivateKey) receiverKey).setProvider("BC"). It reads the algorithm and its parameters from the envelope, so PKCS#1 v1.5 and OAEP both work. This matches the existingKeyAgreebranch next to it, which already uses the JCE recipient. Sending is unchanged.Tests
The new
KeyTransportDecryptionTestencrypts a part to a generated key in three ways (PKCS#1 v1.5, OAEP with default SHA-1 parameters, OAEP with SHA-256) and asserts thatBCCryptoHelper.decryptrecovers the payload.master, both OAEP cases fail withblock incorrect../mvnw -pl Server -am test: 249 tests run, 0 failures (1 skipped, as before).We are running this change on 4.8.3 on our own AS2 host, where it now decrypts every message from that BizTalk partner.
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