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Reading/Writing JSON Web Keys (JWK) in R

2026-05-11

Source: vignettes/jwk.Rmd
jwk.Rmd

RSA / ECDSA keys

JSON Web Keys (JWK) is a format specified in RFC7517 for storing RSA/EC/AES keys in a JSON based format. It can be used to import/export such keys in the browser using the new W3C WebCryptoAPI.

The jose package makes it easy to read/write such keys in R for use with JWT or any other functionality from the openssl package.

Linking to: OpenSSL 3.0.13 30 Jan 2024
library(jose)

# Generate a ECDSA key
key <- openssl::ec_keygen()
jsonlite::prettify(write_jwk(key))
{
    "kty": "EC",
    "crv": "P-256",
    "x": "AwhlUGqqcoas56TmMklF1wp51UenCO3DTnU6jpsvBYo",
    "y": "z2CDULCD3R6d4kLWzPb7PH3xVOxD6n5_vBtKbB2Nqyw",
    "d": "LZxFR1xs0lPzUnQAndNkpvgqM9SL5taovNQHl1z1EOE"
}
 
# Use public key
pubkey <- as.list(key)$pubkey
json <- write_jwk(pubkey)
jsonlite::prettify(json)
{
    "kty": "EC",
    "crv": "P-256",
    "x": "AwhlUGqqcoas56TmMklF1wp51UenCO3DTnU6jpsvBYo",
    "y": "z2CDULCD3R6d4kLWzPb7PH3xVOxD6n5_vBtKbB2Nqyw"
}
 
# Read JWK key
(out <- read_jwk(json))
[256-bit ecdsa public key]
md5: 8303badff3a80c8109fee5b96bafabc8
sha256: 56d6c6a8f1603b7e76eb703948b52fe895bd40a127cd3b014276d939c7a192c8
identical(pubkey, out)
[1] TRUE

AES/HMAC keys

JWT also specifies a format for encoding AES/HMAC secrets. Such secret keys are simply raw bytes.

# Random secret
(key <- rand_bytes(16))
 [1] 5a c7 ec 29 8f 59 d8 e5 b2 f9 73 e9 f7 a4 88 fe
(jwk <- write_jwk(key))
{"kty":"oct","k":"WsfsKY9Z2OWy-XPp96SI_g"} 
 [1] 5a c7 ec 29 8f 59 d8 e5 b2 f9 73 e9 f7 a4 88 fe