No serializer found for class sun.security.util.ObjectIdentifier

First, let's invent a functional implementation for your generateRSA method:

public class SecurityOperations {
    public static KeyPair generateRSAKeys(int keySize) {
        try {
            KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
            keyPairGenerator.initialize(keySize);
            return keyPairGenerator.genKeyPair();
        } catch (NoSuchAlgorithmException e) {
            throw new AssertionError(e);
        }
    }
}

The KeyPair object of Java can not be serialized as JSON by Jackson, so we need to mount another object to do this. Taking a look at what's inside the object KeyPair according with javadocs, considering that the implementation of PublicKey will be a RSAPublicKey and PrivateKey will be a RSAPrivateCrtKey methods getEncoded() are responsible for turning the key into an array of bytes. Other methods can also be seen as exemplified below:

public static void mostrar(KeyPair k) {
    Base64.Encoder b64e = Base64.getEncoder();
    RSAPublicKey pu = (RSAPublicKey) k.getPublic();
    RSAPrivateCrtKey pr = (RSAPrivateCrtKey) k.getPrivate();
    System.out.println("public algorithm: " + pu.getAlgorithm());
    System.out.println("public encoded: " + Arrays.toString(pu.getEncoded()));
    System.out.println("public encoded b64: " + new String(b64e.encode(pu.getEncoded()), StandardCharsets.UTF_8));
    System.out.println("public format: " + pu.getFormat());
    System.out.println("public modulus: " + pu.getModulus());
    System.out.println("public exponent: " + pu.getPublicExponent());
    System.out.println("private algorithm: " + pr.getAlgorithm());
    System.out.println("private encoded: " + Arrays.toString(pr.getEncoded()));
    System.out.println("private encoded b64: " + new String(b64e.encode(pr.getEncoded()), StandardCharsets.UTF_8));
    System.out.println("private format: " + pr.getFormat());
    System.out.println("private modulus: " + pr.getModulus());
    System.out.println("private public exponent: " + pr.getPublicExponent());
    System.out.println("private exponent: " + pr.getPrivateExponent());
    System.out.println("private prime P: " + pr.getPrimeP());
    System.out.println("private prime Q: " + pr.getPrimeQ());
    System.out.println("private prime exponent P: " + pr.getPrimeExponentP());
    System.out.println("private prime exponent Q: " + pr.getPrimeExponentQ());
    System.out.println("private CRT coefficient: " + pr.getCrtCoefficient());
}

public static void main(String[] args) {
    KeyPair kp = SecurityOperations.generateRSAKeys(2048);
    mostrar(kp);
}

Here is the output produced (it will probably vary, since the keys are randomly generated):

public algorithm: RSA
public encoded: [48, -126, 1, 34, 48, 13, 6, 9, 42, -122, 72, -122, -9, 13, 1, 1, 1, 5, 0, 3, -126, 1, 15, 0, 48, -126, 1, 10, 2, -126, 1, 1, 0, -105, 64, -21, -13, 48, -41, 15, -101, 95, 88, -51, -98, 3, 87, 39, 69, 107, 34, -112, -23, 95, -115, 77, 51, -44, -76, 127, -79, -31, 54, -44, -17, -80, -41, 26, -111, 81, -110, -92, 104, -37, 18, -39, 77, -50, 112, -93, -62, -78, 20, 8, 53, 32, -127, -7, -34, -25, 47, -118, 126, -61, -84, -96, 113, -107, 125, -105, 117, 55, -128, -37, 119, 109, 83, 36, 14, 124, -118, 125, 127, 124, 74, 6, 23, 26, 101, 44, -42, -103, -115, -41, 30, -86, 124, 72, 3, -83, -93, -61, -97, 17, 2, -100, -100, 55, -56, 6, 27, 105, 50, -106, 34, 11, -124, -69, -56, 46, 103, -13, 92, -103, -81, -63, 118, -63, 85, -107, 122, -55, 7, 28, -13, 115, 115, 78, 32, 5, 27, -28, -101, -16, 56, -47, 55, -8, 110, 104, 75, -100, -54, 42, -28, -128, 48, -52, 80, -97, -20, -84, -53, -126, -54, 110, -79, 113, 107, -71, 42, -71, -123, 27, 12, 26, -80, 102, 124, 64, 100, -21, -44, 28, 38, 39, 89, -52, 37, 46, 118, 19, 43, 42, -85, 120, -128, -113, -54, -22, 7, 55, -100, 112, -105, 84, -56, 88, -67, -72, -124, 105, -12, 112, 76, -112, -117, -111, -90, 126, -92, 59, -6, 116, -111, 109, 73, 118, 86, -16, -61, 119, 79, -38, 97, -16, -125, -81, 67, 42, 71, 0, 111, 45, 126, -123, 82, 59, -14, -27, 35, 107, -60, 60, 47, -48, -117, -111, -35, 2, 3, 1, 0, 1]
public encoded b64: MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAl0Dr8zDXD5tfWM2eA1cnRWsikOlfjU0z1LR/seE21O+w1xqRUZKkaNsS2U3OcKPCshQINSCB+d7nL4p+w6ygcZV9l3U3gNt3bVMkDnyKfX98SgYXGmUs1pmN1x6qfEgDraPDnxECnJw3yAYbaTKWIguEu8guZ/Ncma/BdsFVlXrJBxzzc3NOIAUb5JvwONE3+G5oS5zKKuSAMMxQn+ysy4LKbrFxa7kquYUbDBqwZnxAZOvUHCYnWcwlLnYTKyqreICPyuoHN5xwl1TIWL24hGn0cEyQi5GmfqQ7+nSRbUl2VvDDd0/aYfCDr0MqRwBvLX6FUjvy5SNrxDwv0IuR3QIDAQAB
public format: X.509
public modulus: 19093998123240252180582981692150144828830602901797443454519587825183993619017054481175293838417376823489124484356227417822926340061836799578918821120350733238600269437402822692122921155415438777156119457909139578459186074935896528785696831008218655198210881466235062369049263837293988599114822903617658097938619169676862043291486270178383148786736245093111668396013934934678252254734808521433323949822262053901441665722210528585024303410822707682321439608316841995757619747917646039475558643433789028709687382507498557032525353420421280426426441628371937858875882959460301371729699031347236517313006952994100973638109
public exponent: 65537
private algorithm: RSA
private encoded: [48, -126, 4, -68, 2, 1, 0, 48, 13, 6, 9, 42, -122, 72, -122, -9, 13, 1, 1, 1, 5, 0, 4, -126, 4, -90, 48, -126, 4, -94, 2, 1, 0, 2, -126, 1, 1, 0, -105, 64, -21, -13, 48, -41, 15, -101, 95, 88, -51, -98, 3, 87, 39, 69, 107, 34, -112, -23, 95, -115, 77, 51, -44, -76, 127, -79, -31, 54, -44, -17, -80, -41, 26, -111, 81, -110, -92, 104, -37, 18, -39, 77, -50, 112, -93, -62, -78, 20, 8, 53, 32, -127, -7, -34, -25, 47, -118, 126, -61, -84, -96, 113, -107, 125, -105, 117, 55, -128, -37, 119, 109, 83, 36, 14, 124, -118, 125, 127, 124, 74, 6, 23, 26, 101, 44, -42, -103, -115, -41, 30, -86, 124, 72, 3, -83, -93, -61, -97, 17, 2, -100, -100, 55, -56, 6, 27, 105, 50, -106, 34, 11, -124, -69, -56, 46, 103, -13, 92, -103, -81, -63, 118, -63, 85, -107, 122, -55, 7, 28, -13, 115, 115, 78, 32, 5, 27, -28, -101, -16, 56, -47, 55, -8, 110, 104, 75, -100, -54, 42, -28, -128, 48, -52, 80, -97, -20, -84, -53, -126, -54, 110, -79, 113, 107, -71, 42, -71, -123, 27, 12, 26, -80, 102, 124, 64, 100, -21, -44, 28, 38, 39, 89, -52, 37, 46, 118, 19, 43, 42, -85, 120, -128, -113, -54, -22, 7, 55, -100, 112, -105, 84, -56, 88, -67, -72, -124, 105, -12, 112, 76, -112, -117, -111, -90, 126, -92, 59, -6, 116, -111, 109, 73, 118, 86, -16, -61, 119, 79, -38, 97, -16, -125, -81, 67, 42, 71, 0, 111, 45, 126, -123, 82, 59, -14, -27, 35, 107, -60, 60, 47, -48, -117, -111, -35, 2, 3, 1, 0, 1, 2, -126, 1, 0, 10, -8, -56, -92, -31, 124, 24, 67, -69, 12, -28, 13, 124, 76, -116, 42, -70, -12, -52, -14, 64, -34, 45, 37, 127, 94, -128, -116, -44, -69, 119, -126, -45, -97, 38, -20, 55, -80, -99, -128, -123, -77, -66, 83, -88, -113, -1, 49, 22, 93, -31, -94, -120, -13, 36, -65, 8, -94, 40, 55, -67, -43, -3, -27, 127, 100, -106, -30, 7, -34, -81, 12, -32, -65, 81, 52, 67, -48, 127, -2, 9, 116, 13, 49, 11, -41, 31, 3, -118, 44, 1, -40, -43, -95, 34, 80, 49, -2, 89, 40, 102, -63, 123, -66, -47, 69, 15, 60, 89, -53, 51, -100, -48, -99, 22, 74, 21, 35, -79, 65, -100, 92, 101, 122, 73, -41, -3, 121, -57, -69, -80, -7, 78, -110, 14, -107, -87, -2, -117, -24, -95, -12, -97, -100, 37, 38, 46, -19, 90, -88, 109, 114, 15, -43, -47, -110, -49, 63, -76, 52, 43, -77, -53, 33, -79, 62, 39, -122, -56, 98, -119, -80, 125, -81, -51, -78, -15, 126, -1, -99, 77, 108, -52, 109, 27, 8, -44, 25, 33, -97, 124, -71, -126, -90, -46, -36, -36, -41, 21, -19, -124, -120, 25, 26, 21, 23, -53, -39, 49, -126, 22, 34, 82, 37, 1, 27, -103, 64, -104, 123, 46, -20, 87, 2, -62, 31, 46, -41, 41, -92, 48, -16, 13, -14, 44, 88, -101, 69, 33, 48, 25, -106, -44, -12, 27, -59, -88, 60, 27, 51, -111, -16, -127, 77, -111, -71, 2, -127, -127, 0, -24, -63, 108, -119, -24, 100, 121, 53, 72, 31, -5, 118, 38, 69, -97, 61, 108, -29, 20, -29, 88, -119, -108, 116, 34, -23, 80, -40, -22, 91, 59, 8, -112, 113, 13, 4, 114, -123, 18, 70, 79, 109, -47, 96, 32, -108, 67, -59, 72, -92, 66, 20, -107, 65, 17, -126, 12, -18, -102, 115, -114, 78, 46, -68, -81, 75, -89, 43, 82, 18, -38, 55, -125, -28, 103, -124, -86, -55, -117, 89, 76, 9, 32, -52, 123, -100, -35, -126, 16, -92, -121, 29, -2, -125, 6, -106, 10, 116, 61, -19, 17, 101, -30, 89, 19, 43, 42, 100, 116, -9, -44, -13, 6, -48, -101, 119, 76, 45, -128, -71, -89, 19, 57, 53, -7, -94, 61, 47, 2, -127, -127, 0, -90, 91, -42, 68, -68, 24, 90, -51, 50, -108, 106, -36, 116, 11, -31, -77, -93, 111, -119, 16, -15, -5, 112, -128, -86, 101, -30, -101, -11, -97, 11, 61, 48, -103, -39, 36, 50, -74, 92, -121, -107, 53, 2, 54, 75, -70, -49, 25, -87, -56, 36, 102, -98, -107, 73, -35, -50, -98, 31, -106, -15, 99, -23, 118, 105, -115, 91, 4, 51, 66, 76, 33, 67, -39, 18, 105, 37, -17, -47, 91, 19, -43, -109, 28, -5, -33, -3, 60, -64, 14, 11, 118, -128, -94, -21, -35, 120, 125, 77, 93, -37, 114, -73, 20, 59, -83, 122, 70, 3, 20, -4, -28, -109, -70, 96, -104, -87, -85, -7, -106, -75, -123, -6, 118, -76, 3, 86, -77, 2, -127, -128, 8, 118, -104, 10, -65, -81, 127, -108, -57, 101, -102, 80, 38, 126, 27, -105, 49, 49, 100, -98, 11, -89, 29, 5, -56, 11, 49, -52, 97, 97, 37, -39, 94, -33, 45, 120, -2, -19, 5, -56, 22, -75, 72, -118, -75, 68, -114, -34, 74, -112, -26, 114, 55, 39, 33, -118, -40, 11, -119, 4, 48, -91, 121, 31, -107, 68, 43, -12, -16, 76, 13, 49, 61, -109, 125, -116, 30, 101, -85, -78, 120, -120, 80, 111, -1, 2, -86, 47, 67, -119, -89, -4, 24, 56, 13, 114, 65, 57, 14, -45, 98, -15, -112, 116, 106, -75, 4, 26, -103, 2, 53, -11, 12, 71, 99, -113, -57, -18, 83, -94, -20, -121, 79, 106, 62, 4, 127, 51, 2, -127, -128, 110, -74, -16, 3, 14, -85, -90, -62, -87, -58, -36, -41, -102, -29, -51, 114, 32, 115, 58, 101, 108, -90, 74, 89, 87, 14, 55, -94, 83, -11, 101, 37, 116, 18, -17, -48, -121, 111, -106, 101, 37, -120, 1, -48, -32, -43, -110, -65, 33, -97, 113, -102, 90, 48, 64, -40, -67, -119, -66, -68, 86, 42, -120, 85, -90, 41, -51, 73, 30, 84, 33, 22, -126, 113, 21, 47, -91, 111, -43, -123, 39, -50, 27, -6, 78, 38, -28, 2, 106, 78, -18, -110, 15, 74, 94, 111, 38, -95, 61, -68, 25, 48, 95, 103, -73, -49, -36, 112, 123, -36, -101, -14, 3, -33, 38, 42, 115, -63, 96, 122, 76, -108, -67, -4, 2, 17, -74, -63, 2, -127, -128, 55, -34, 14, 14, 81, -114, 43, 103, 33, 91, 26, 24, -9, 4, 80, 117, 20, -66, 124, -27, -31, 121, -88, -92, -42, 77, 25, -57, -76, 25, -37, -28, 31, 110, 46, 101, -2, 121, 9, -48, -33, -101, -53, -54, -127, 16, -75, 10, 20, -27, -68, 16, 25, -85, -26, -90, -26, 56, 112, 61, 64, -68, -120, 127, -89, -66, 21, -59, 12, -19, -49, 26, -58, -81, -70, 15, -111, -104, 58, -92, 2, 76, 119, 36, 107, 94, 52, 127, 82, -19, -17, 106, -119, -56, -113, -50, 85, 40, -79, -47, -64, 66, 9, 8, -56, 69, 57, -128, 67, -46, 82, -4, -122, 82, -116, -1, -33, 67, -35, -27, 56, -25, 64, 16, -68, 59, -65, 91]
private encoded b64: MIIEvAIBADANBgkqhkiG9w0BAQEFAASCBKYwggSiAgEAAoIBAQCXQOvzMNcPm19YzZ4DVydFayKQ6V+NTTPUtH+x4TbU77DXGpFRkqRo2xLZTc5wo8KyFAg1IIH53ucvin7DrKBxlX2XdTeA23dtUyQOfIp9f3xKBhcaZSzWmY3XHqp8SAOto8OfEQKcnDfIBhtpMpYiC4S7yC5n81yZr8F2wVWVeskHHPNzc04gBRvkm/A40Tf4bmhLnMoq5IAwzFCf7KzLgspusXFruSq5hRsMGrBmfEBk69QcJidZzCUudhMrKqt4gI/K6gc3nHCXVMhYvbiEafRwTJCLkaZ+pDv6dJFtSXZW8MN3T9ph8IOvQypHAG8tfoVSO/LlI2vEPC/Qi5HdAgMBAAECggEACvjIpOF8GEO7DOQNfEyMKrr0zPJA3i0lf16AjNS7d4LTnybsN7CdgIWzvlOoj/8xFl3hoojzJL8Ioig3vdX95X9kluIH3q8M4L9RNEPQf/4JdA0xC9cfA4osAdjVoSJQMf5ZKGbBe77RRQ88WcsznNCdFkoVI7FBnFxleknX/XnHu7D5TpIOlan+i+ih9J+cJSYu7VqobXIP1dGSzz+0NCuzyyGxPieGyGKJsH2vzbLxfv+dTWzMbRsI1Bkhn3y5gqbS3NzXFe2EiBkaFRfL2TGCFiJSJQEbmUCYey7sVwLCHy7XKaQw8A3yLFibRSEwGZbU9BvFqDwbM5HwgU2RuQKBgQDowWyJ6GR5NUgf+3YmRZ89bOMU41iJlHQi6VDY6ls7CJBxDQRyhRJGT23RYCCUQ8VIpEIUlUERggzumnOOTi68r0unK1IS2jeD5GeEqsmLWUwJIMx7nN2CEKSHHf6DBpYKdD3tEWXiWRMrKmR099TzBtCbd0wtgLmnEzk1+aI9LwKBgQCmW9ZEvBhazTKUatx0C+Gzo2+JEPH7cICqZeKb9Z8LPTCZ2SQytlyHlTUCNku6zxmpyCRmnpVJ3c6eH5bxY+l2aY1bBDNCTCFD2RJpJe/RWxPVkxz73/08wA4LdoCi6914fU1d23K3FDutekYDFPzkk7pgmKmr+Za1hfp2tANWswKBgAh2mAq/r3+Ux2WaUCZ+G5cxMWSeC6cdBcgLMcxhYSXZXt8teP7tBcgWtUiKtUSO3kqQ5nI3JyGK2AuJBDCleR+VRCv08EwNMT2TfYweZauyeIhQb/8Cqi9Diaf8GDgNckE5DtNi8ZB0arUEGpkCNfUMR2OPx+5TouyHT2o+BH8zAoGAbrbwAw6rpsKpxtzXmuPNciBzOmVspkpZVw43olP1ZSV0Eu/Qh2+WZSWIAdDg1ZK/IZ9xmlowQNi9ib68ViqIVaYpzUkeVCEWgnEVL6Vv1YUnzhv6TibkAmpO7pIPSl5vJqE9vBkwX2e3z9xwe9yb8gPfJipzwWB6TJS9/AIRtsECgYA33g4OUY4rZyFbGhj3BFB1FL585eF5qKTWTRnHtBnb5B9uLmX+eQnQ35vLyoEQtQoU5bwQGavmpuY4cD1AvIh/p74VxQztzxrGr7oPkZg6pAJMdyRrXjR/Uu3vaonIj85VKLHRwEIJCMhFOYBD0lL8hlKM/99D3eU450AQvDu/Ww==
private format: PKCS#8
private modulus: 19093998123240252180582981692150144828830602901797443454519587825183993619017054481175293838417376823489124484356227417822926340061836799578918821120350733238600269437402822692122921155415438777156119457909139578459186074935896528785696831008218655198210881466235062369049263837293988599114822903617658097938619169676862043291486270178383148786736245093111668396013934934678252254734808521433323949822262053901441665722210528585024303410822707682321439608316841995757619747917646039475558643433789028709687382507498557032525353420421280426426441628371937858875882959460301371729699031347236517313006952994100973638109
private public exponent: 65537
private exponent: 1385062896957202173832972137334357515849988345440667808761251209559862454259533957970418952772269243616084010538009142077455358357171859334394007592751382971700042432601629904914054155253444557221114666568504044371804791190400111354611940348399705308639311083670010627621957066733228890553303753357620071068234175206467715071430957112047097648304499050663377930133554042365863403753737570076381030070520699317037698947196347863859272622193490216279446699486953429387881067902697902595959388326081303450064822132405216055743367243667023940226146997997801295602085346286980230520369315767210190391626311296904332153273
private prime P: 163446514321073004442310556270960412203771433624655158721006609579827500850107863546845692572650063382225022074429964559294811733212783258552058786426329332982667733134837610861879996684888893357686279366658034746022149419467787909834301728035554629464902772892485459762980590312425691200796671107481328565551
private prime Q: 116821078764225937786358391100274496338962030684783660691596546694640594900960832456149362059936965037369846024219972954264378122562644595349923871054066112124223881181817170214143427412259330933217289911677576420863099026572813515624324206650665200409325298134954454748913677165300046201395480989434281940659
private prime exponent P: 5943101509484977487312908060999109850642954763378751594246894893399590071651235772649545835186613684481166785226156301704373657021927499048317074142147837107247771610850634400168760121764655581905891385488290535114069641066752194777532401817427204205484891096675051507014095041190631584166172806950699695923
private prime exponent Q: 77746435927498642026485917668333497601662693293063828749022307713710487010395771372009865810247809131786978412078342621316128541033192039165391756715964227023057948969683349803318426690466499503840659730957004030888886081801117449646314671060247087615440624432826853507615834463611804249814079052064721319617
private CRT coefficient: 39231423826464180962220915291000320841879655929334305881366464052655074878611840446781910148747551748349989044895551744049159735078739671304472930837060362338022547504311898612471588078035380996563722887816479784108365174533582035576898575410992828487201106190178397938016504118904196690718456301943464378203

While seeing this bunch of information is legal, what you really need is just the methods getEncoded() . However, you still need to be able to rebuild KeyPair from these byte arrays. To facilitate, as you can see in the code, I'm already using Base64 to convert byte[] to String that can be easily transported in JSON.

So, to rebuild KeyPair from Base64-encoded strings, you can do this in the SecurityOperations class:

private static final Base64.Decoder b64d = Base64.getDecoder();
private static final KeyFactory keyFactory;

static {
    try {
        keyFactory = KeyFactory.getInstance("RSA");
    } catch (NoSuchAlgorithmException e) {
        throw new AssertionError(e);
    }
}

private static RSAPublicKey rebuildPublicKey(String base64key) {
    try {
        byte[] b = b64d.decode(base64key.getBytes(StandardCharsets.UTF_8));
        return (RSAPublicKey) keyFactory.generatePublic(new X509EncodedKeySpec(b));
    } catch (InvalidKeySpecException e) {
        throw new IllegalArgumentException(e);
    }
}

private static RSAPrivateCrtKey rebuildPrivateKey(String base64key) {
    try {
        byte[] b = b64d.decode(base64key.getBytes(StandardCharsets.UTF_8));
        return (RSAPrivateCrtKey) keyFactory.generatePrivate(new PKCS8EncodedKeySpec(b));
    } catch (InvalidKeySpecException e) {
        throw new IllegalArgumentException(e);
    }
}

public static KeyPair rebuildKey(String base64PublicKey, String base64PrivateKey) {
    return new KeyPair(rebuildPublicKey(base64PublicKey), rebuildPrivateKey(base64PrivateKey));
}

Then, how to convert KeyPair to two strings and vice versa, we use a class to group them together:

public final class EncodedKeyPair {
    private static final Base64.Encoder b64e = Base64.getEncoder();
    private final String base64PublicKey;
    private final String base64PrivateKey;

    public EncodedKeyPair(KeyPair kp) {
        this.base64PublicKey = new String(b64e.encode(kp.getPublic().getEncoded()), StandardCharsets.UTF_8);
        this.base64PrivateKey = new String(b64e.encode(kp.getPrivate().getEncoded()), StandardCharsets.UTF_8);
    }

    @JsonCreator
    public EncodedKeyPair(
            @JsonProperty("base64PublicKey") int base64PublicKey,
            @JsonProperty("base64PrivateKey") int base64PrivateKey)
    {
        this.base64PublicKey = base64PublicKey;
        this.base64PrivateKey = base64PrivateKey;
    }

    public KeyPair rebuild() {
        return SecurityOperations.rebuildKey(base64PublicKey, base64PrivateKey);
    }
}

Jackson uses attribute-based serialization, without making use of getters and setters. For deserialization, Jackson will use the constructor annotated with @JsonCreator .

To test this all:

public static void main(String[] args) {
    KeyPair kp = SecurityOperations.generateRSAKeys(2048);
    mostrar(kp);
    System.out.println();
    mostrar(new EncodedKeyPair(kp).rebuild());
}

And you will notice that the two outputs are the same.

See this running on Coding Ground.

Finally, you do this change the generateRSAKeys method in your controller:

@RequestMapping(value = "/request-RSA-keys", method = RequestMethod.PUT)
public static EncodedKeyPair generateRSAKeys(@RequestBody String sizeKey) {
    return new EncodedKeyPair(SecurityOperations.generateRSAKeys(Integer.parseInt(sizeKey)));
}

And in your controller, you can delete this:

@Autowired
private SecurityOperations securityOperations;

The reason is SecurityOperations does not need to be injected, since you use its static methods instead of using a Spring managed instance.

Finally, I make one important point: Exporting the private key (which is inside KeyPair ) is almost always a bad idea. Ideally, you should not export the private key ever! Only the public key should be exported.