AWS Cognito解码JWKS.json

Question

I am working on verifying the access token on AWS Cognito. One thing I have to do is to convert the key from jwks.json (of the userpool) into a rsa Public Key structure (depending on the used JWT API).

So the values for 'n' and 'e' must be big int (long) and int.

What would be the proper value of those two variables, for example: raw_n := "rdTmzrh7t0i_YN0MDLejnS0jXIFoSzRfFEbqf-bwGuRLnhLI4T3zGAk9HGZeAG6B5gg1D40Jsz1upo4E70VS0raGfSBPYPO7ZAJ2VCUUeblr9X_aWK4f294v4Cf3n8jZyFcGK9qhgcqy3DlHqqDANtjamWVtEhTRTFc-qoz1ScvHmPupsXlj1FsAEFEbVhP4705ez5gW3uQOoidrm38sPFwCN7g7xhA9CyzF04Zsjky55OfMCyWlIt7nljLx7ZRG3dVRD3vdEBI99qtxf43qMCWSPUk7Whn11Wf_u0xDrWhtGR9k599rKBBRWuqcujYYnFuOT0BeQIL25cePPK8lxw" raw_e := "AQAB"

I suppose this is Base64 URL encoded. I am using Go and when decoding them, I am having those values:

Value of N = 21944212446918148307583266513211511961176501179660110972882270757464120247554839864039423096862533136364974693915136668416630333929475539217929135693935014796040215031370110392351836608149288005498214604075814317642291632460369313969964278103135047317799644939426174469533574133378199425168189176269507635563270873057483981163804984573367938044175828995131343800369166239708527999544583873649523245709447765091038652758632917341001616695912404965678061555823269517387737693508193881028187912513285002546706797506255288735805912213209305939523528571103281920754204216834697552752238593850648051945624431639572960454087 Value of E = 65537

And the final values are: TokenSignature= GYZQKv7o8_o9E4ktVKZngYD4BS5QluOMwE-MRcJB432CmNimQm6JbvT3H48ECThe4f3sZ1KyVbgDJbyUnlkaAwMEBjMnlV7AUaZb-ifveM7kHM30BS5LCV_SCiCk-PvmWjeIHu9bR3EwG8azJCceD5A7gDLmhAtPN94gRy-opXJPAnaCba00AwKBd_pN3UH7LYu4u4EQ29eIfn4k4RCLuR31jr7ad3dvvjhhy658dQSHzSuPZGcN1-CRVSlrd0nk0Ba2t8W33LtjxM6wzPThWgh0fpy2XEDosGU_9FiXdEjUKisE3VHxroygQ8ekVWKHssa2eujXCx8OthWzaGag0w1 Signing String= eyJhbGciOiJSUzI1NiIsImtpZCI6ImpBNlFvakp0RkI0TmNIR1BmcS85ZWgzSHI2YnVXWEI0VzkxRTd5bWNjSk09In0.eyJleHAiOjE0NzAyNzgzMTEsInRva2VuX3VzZSI6ImFjY2VzcyIsImlzcyI6Imh0dHBzOi8vY29nbml0by1pZHAudXMtZWFzdC0xLmFtYXpvbmF3cy5jb20vdXMtZWFzdC0xX0d1OFlhVGg3MiIsImNsaWVudF9pZCI6IjRwNzNuYjhra3NsbHJrbTlzMzdzYXZsNzEzIiwidXNlcm5hbWUiOiJtYXRlbyIsImtpZCI6IiIsImFsZyI6IiIsImp0aSI6IjhmNTBiZmU4LWVlNGUtNGFkZi04MDQxLWU5MGM4YWJkZDExZCIsImlhdCI6MTQ3MDI3NDcxMSwic3ViIjoiYjFjMDZhMTktYjE5Yy00NGMwLTgzZjctODY2NTZjYzRmMjMxIn0 rsa.PublicKey{N:21944212446918148307583266513211511961176501179660110972882270757464120247554839864039423096862533136364974693915136668416630333929475539217929135693935014796040215031370110392351836608149288005498214604075814317642291632460369313969964278103135047317799644939426174469533574133378199425168189176269507635563270873057483981163804984573367938044175828995131343800369166239708527999544583873649523245709447765091038652758632917341001616695912404965678061555823269517387737693508193881028187912513285002546706797506255288735805912213209305939523528571103281920754204216834697552752238593850648051945624431639572960454087, E:65537}

However, with those revisiter values, I am still getting crypto/rsa: verification error. How can I determine if the problem is coming from the JWT Library or the values?

Thank you very much

Answer 1

You should be able to verify the signature with the rsa.PublicKey generated by the program below or at https://play.golang.org/p/VZqD5m057b. It is based on code from https://github.com/mendsley/gojwk (please see the playground link or https://github.com/mendsley/gojwk/blob/master/LICENSE for the Copyright attribution) - I would recommend to clone that repository and use it as an example and model.

package main

import (
    "crypto/rsa"
    "encoding/base64"
    "encoding/binary"
    "fmt"
    "math/big"
)

func main() {
    rawN := "rdTmzrh7t0i_YN0MDLejnS0jXIFoSzRfFEbqf-bwGuRLnhLI4T3zGAk9HGZeAG6B5gg1D40Jsz1upo4E70VS0raGfSBPYPO7ZAJ2VCUUeblr9X_aWK4f294v4Cf3n8jZyFcGK9qhgcqy3DlHqqDANtjamWVtEhTRTFc-qoz1ScvHmPupsXlj1FsAEFEbVhP4705ez5gW3uQOoidrm38sPFwCN7g7xhA9CyzF04Zsjky55OfMCyWlIt7nljLx7ZRG3dVRD3vdEBI99qtxf43qMCWSPUk7Whn11Wf_u0xDrWhtGR9k599rKBBRWuqcujYYnFuOT0BeQIL25cePPK8lxw"
    rawE := "AQAB"
    decodedE, err := base64.RawURLEncoding.DecodeString(rawE)
    if err != nil {
        panic(err)
    }
    // make sure that the E field is at least 4 bytes, pad if necessary
    if len(decodedE) < 4 {
        ndata := make([]byte, 4)
        copy(ndata[4-len(decodedE):], decodedE)
        decodedE = ndata
    }
    pubKey := &rsa.PublicKey{
        N: &big.Int{},
        E: int(binary.BigEndian.Uint32(decodedE[:])),
    }
    decodedN, err := base64.RawURLEncoding.DecodeString(rawN)
    if err != nil {
        panic(err)
    }
    pubKey.N.SetBytes(decodedN)
    fmt.Println(decodedN)
    fmt.Println(decodedE)
    fmt.Printf("%#v
", *pubKey)
}

Output:

[173 212 230 206 184 123 183 72 191 96 221 12 12 183 163 157 45 35 92 129 104 75 52 95 20 70 234 127 230 240 26 228 75 158 18 200 225 61 243 24 9 61 28 102 94 0 110 129 230 8 53 15 141 9 179 61 110 166 142 4 239 69 82 210 182 134 125 32 79 96 243 187 100 2 118 84 37 20 121 185 107 245 127 218 88 174 31 219 222 47 224 39 247 159 200 217 200 87 6 43 218 161 129 202 178 220 57 71 170 160 192 54 216 218 153 101 109 18 20 209 76 87 62 170 140 245 73 203 199 152 251 169 177 121 99 212 91 0 16 81 27 86 19 248 239 78 94 207 152 22 222 228 14 162 39 107 155 127 44 60 92 2 55 184 59 198 16 61 11 44 197 211 134 108 142 76 185 228 231 204 11 37 165 34 222 231 150 50 241 237 148 70 221 213 81 15 123 221 16 18 61 246 171 113 127 141 234 48 37 146 61 73 59 90 25 245 213 103 255 187 76 67 173 104 109 25 31 100 231 223 107 40 16 81 90 234 156 186 54 24 156 91 142 79 64 94 64 130 246 229 199 143 60 175 37 199] [0 1 0 1] rsa.PublicKey{N:21944212446918148307583266513211511961176501179660110972882270757464120247554839864039423096862533136364974693915136668416630333929475539217929135693935014796040215031370110392351836608149288005498214604075814317642291632460369313969964278103135047317799644939426174469533574133378199425168189176269507635563270873057483981163804984573367938044175828995131343800369166239708527999544583873649523245709447765091038652758632917341001616695912404965678061555823269517387737693508193881028187912513285002546706797506255288735805912213209305939523528571103281920754204216834697552752238593850648051945624431639572960454087, E:65537}