Sorry for my mistake, i forget to post my private key. the following is my private key 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 The encryption code is status = SecKeyEncrypt(key, kSecPaddingNone, [dataSegment bytes], dataSegmentRealSize, cipherBuffer, &cipherBufferSize );

@kxdev Thanks for your reply and is very helpful for me. Can I understand that my app has enabled Keychain sharing in "signing and capabilities" and my code does not set kSecAttrSynchronizable. So the data I added using SecItemAdd will not be migrate or sync during device to device transfer (e.g. using Quick Start)?