Decrypt a ciphertext

decrypt dispatches on both arguments and accepts them in either order, as the C++ header does: Decrypt(ciphertext, privateKey) is the primary form and Decrypt(privateKey, ciphertext) forwards to it (cryptocontext.h, both overloads). The key-first order lets code that is written around the holder of the key, such as a party object in a protocol, put that holder first, the same way encrypt() puts the key first.

Usage

decrypt(ct, key, ...)

Arguments

ct

A Ciphertext, or a PrivateKey when the key-first order is used.

key

A PrivateKey, or a Ciphertext when the key-first order is used.

...

Additional arguments (cc = CryptoContext)

Value

A Plaintext

Examples

cc <- fhe_context("CKKS", multiplicative_depth = 2L,
                  scaling_mod_size = 50L, batch_size = 8L)
kp <- key_gen(cc, eval_mult = TRUE)
pt <- make_ckks_packed_plaintext(cc, c(0.25, 0.5, 0.75, 1))
ct <- encrypt(kp@public, pt, cc = cc)

## Add the encrypted vector to itself, then decrypt. Decryption
## returns a Plaintext padded out to the full slot count, so trim it
## back to the length that was encoded.
out <- decrypt(eval_add(ct, ct), kp@secret, cc = cc)
out <- set_length(out, 4L)
get_real_packed_value(out)
#> [1] 0.5 1.0 1.5 2.0

## The same call with the key first:
out2 <- decrypt(kp@secret, eval_add(ct, ct), cc = cc)
get_real_packed_value(set_length(out2, 4L))
#> [1] 0.5 1.0 1.5 2.0