Introduce PK_Decryptor(_EME)::ciphertext_length()#5717
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In general this accessor is likely not very useful, because the expected plaintext size might not be known upfront. However, there are use cases where it is and we need a way to query the expected ciphertext length for a certain asymmetric algorithm. Also, this provides consistency with PK_KEM_Decryptor::encapsulated_key_length()
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Jul 8, 2026
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Interface looks fine. Unfortunate about having to create new cipher objects in DLIES/ECIES but given we allow CBC or indeed effectively arbitrary transforms here, would be hard to do anything else without some kind of significant refactoring, the shape of which I'm not even sure of....
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Yeah, but frankly: I doubt that there's a substantial user base for those. Even less so users that would start actually using this API. 🤷 |
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This allows querying an instance of
PK_Decryptorfor an estimate of the expected ciphertext size given an expected plaintext length. In the general use case that might not be overly useful, assuming that the plaintext size is not known before decryption.However, for many algorithms (most notably RSA or ElGamal) the expected ciphertext size is actually fixed and only dependent on the key length. For those, the new method facilitates an algorithm-agnostic querying of the expected ciphertext size, e.g. for input validation, pre-allocation and such.
Concretely, it comes in handy in the context of #5686 where we need an RSA-to-KEM Adapter and
PK_KEM_Decryptorhas anencapsulated_key_length()accessor that can be implemented conveniently with this new method.Additionally this fixes two confusing typos in the abstract public interface classes.