diff --git a/crates/policy/src/policy/function/binary.rs b/crates/policy/src/policy/function/binary.rs
index 6da39c89d..37638c03a 100644
--- a/crates/policy/src/policy/function/binary.rs
+++ b/crates/policy/src/policy/function/binary.rs
@@ -14,19 +14,394 @@
 
 use std::collections::HashMap;
 
-use serde::{Deserialize, Serialize};
+use serde::{Deserialize, Deserializer, Serialize, Serializer, de};
 
 use super::func::InnerFunc;
 
 pub type BinaryFunc = InnerFunc<BinaryFuncValue>;
 
-// todo implement it
-#[derive(Serialize, Deserialize, Clone, PartialEq, Eq, Debug)]
-#[serde(transparent)]
-pub struct BinaryFuncValue(String);
+#[derive(thiserror::Error, Clone, Debug, Eq, PartialEq)]
+pub enum BinaryFuncValueError {
+    #[error("invalid base64 for BinaryEquals")]
+    InvalidBase64,
+}
 
-impl BinaryFunc {
-    pub fn evaluate(&self, _values: &HashMap<String, Vec<String>>) -> bool {
-        todo!()
+/// Policy value for the AWS IAM `BinaryEquals` condition.
+///
+/// Policies store the value as a base64-encoded string or array of strings.
+/// During deserialization the values are validated and the raw bytes are
+/// cached, so evaluation is a plain byte comparison and malformed policies
+/// are rejected at parse time.
+#[derive(Clone, Debug)]
+pub struct BinaryFuncValue {
+    /// Original base64 forms, preserved for serialization round-trips.
+    encoded: Vec<String>,
+    /// Decoded bytes used for comparison during `evaluate`.
+    decoded: Vec<Vec<u8>>,
+}
+
+impl BinaryFuncValue {
+    /// Construct from a base64-encoded string, validating the encoding.
+    pub fn new(encoded: impl Into<String>) -> Result<Self, BinaryFuncValueError> {
+        Self::from_encoded_values(vec![encoded.into()])
+    }
+
+    fn from_encoded_values(encoded: Vec<String>) -> Result<Self, BinaryFuncValueError> {
+        let decoded = encoded
+            .iter()
+            .map(|value| {
+                base64_simd::STANDARD
+                    .decode_to_vec(value.as_bytes())
+                    .map_err(|_| BinaryFuncValueError::InvalidBase64)
+            })
+            .collect::<Result<Vec<_>, _>>()?;
+        Ok(Self { encoded, decoded })
+    }
+}
+
+impl TryFrom<String> for BinaryFuncValue {
+    type Error = BinaryFuncValueError;
+
+    fn try_from(encoded: String) -> Result<Self, Self::Error> {
+        Self::new(encoded)
+    }
+}
+
+impl TryFrom<&str> for BinaryFuncValue {
+    type Error = BinaryFuncValueError;
+
+    fn try_from(encoded: &str) -> Result<Self, Self::Error> {
+        Self::new(encoded)
+    }
+}
+
+// Equality is defined over decoded bytes so that semantically equal values
+// compare equal regardless of incidental base64 formatting differences.
+impl PartialEq for BinaryFuncValue {
+    fn eq(&self, other: &Self) -> bool {
+        self.decoded == other.decoded
+    }
+}
+
+impl Eq for BinaryFuncValue {}
+
+impl Serialize for BinaryFuncValue {
+    fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
+        if self.encoded.len() == 1 {
+            serializer.serialize_str(&self.encoded[0])
+        } else {
+            self.encoded.serialize(serializer)
+        }
+    }
+}
+
+impl<'de> Deserialize<'de> for BinaryFuncValue {
+    fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
+        struct StringOrVecVisitor;
+
+        impl<'de> de::Visitor<'de> for StringOrVecVisitor {
+            type Value = BinaryFuncValue;
+
+            fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
+                formatter.write_str("a base64 string or an array of base64 strings")
+            }
+
+            fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
+            where
+                E: de::Error,
+            {
+                BinaryFuncValue::new(value).map_err(E::custom)
+            }
+
+            fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+            where
+                A: de::SeqAccess<'de>,
+            {
+                let mut values = Vec::with_capacity(seq.size_hint().unwrap_or(0));
+                while let Some(value) = seq.next_element::<String>()? {
+                    values.push(value);
+                }
+                if values.is_empty() {
+                    return Err(de::Error::custom("empty"));
+                }
+
+                BinaryFuncValue::from_encoded_values(values).map_err(de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_any(StringOrVecVisitor)
+    }
+}
+
+impl BinaryFunc {
+    /// Evaluate an AWS IAM `BinaryEquals` condition.
+    ///
+    /// AWS semantics compare the base64-decoded bytes of the policy value
+    /// against the base64-decoded bytes of the request context value. In this
+    /// codebase request context values come directly from HTTP header strings
+    /// (see `rustfs::auth::get_condition_values_with_query`), so for real
+    /// binary condition keys (e.g. SSE-C customer-key headers) the request
+    /// value is itself base64. Decoding both sides is therefore required for
+    /// the comparison to ever succeed.
+    ///
+    /// All key/value pairs in the function must match (logical AND); for a
+    /// given key, any decoded request value that equals any expected decoded
+    /// policy value satisfies that pair (OR across request values and policy
+    /// values). A missing request key, or *any* request value that is not
+    /// valid base64, causes the condition to evaluate to false (fail-closed).
+    pub fn evaluate(&self, values: &HashMap<String, Vec<String>>) -> bool {
+        for inner in self.0.iter() {
+            let Some(rvalues) = values.get(inner.key.name().as_str()) else {
+                return false;
+            };
+
+            let mut matched = false;
+            for v in rvalues {
+                let Ok(decoded) = base64_simd::STANDARD.decode_to_vec(v.as_bytes()) else {
+                    return false;
+                };
+                if inner
+                    .values
+                    .decoded
+                    .iter()
+                    .any(|expected| decoded.as_slice() == expected.as_slice())
+                {
+                    matched = true;
+                }
+            }
+            if !matched {
+                return false;
+            }
+        }
+
+        true
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{BinaryFunc, BinaryFuncValue, BinaryFuncValueError};
+    use crate::policy::function::func::FuncKeyValue;
+    use crate::policy::function::{
+        key::Key,
+        key_name::AwsKeyName::*,
+        key_name::KeyName::{self, *},
+    };
+    use std::collections::HashMap;
+
+    fn new_func(name: KeyName, variable: Option<String>, value: &str) -> BinaryFunc {
+        BinaryFunc {
+            0: vec![FuncKeyValue {
+                key: Key { name, variable },
+                values: BinaryFuncValue::new(value).expect("valid base64 in test"),
+            }],
+        }
+    }
+
+    fn new_multi_func(name: KeyName, variable: Option<String>, values: &[&str]) -> BinaryFunc {
+        BinaryFunc {
+            0: vec![FuncKeyValue {
+                key: Key { name, variable },
+                values: BinaryFuncValue::from_encoded_values(values.iter().map(|value| (*value).to_string()).collect())
+                    .expect("valid binary array in test"),
+            }],
+        }
+    }
+
+    #[test]
+    fn evaluate_matches_decoded_bytes() {
+        // base64("hello") = "aGVsbG8="
+        let f = new_func(Aws(AWSUsername), None, "aGVsbG8=");
+        let mut ctx = HashMap::new();
+        // Request value is itself base64 — BinaryEquals decodes both sides.
+        ctx.insert("username".to_string(), vec!["aGVsbG8=".to_string()]);
+        assert!(f.evaluate(&ctx));
+    }
+
+    #[test]
+    fn evaluate_rejects_non_matching_value() {
+        let f = new_func(Aws(AWSUsername), None, "aGVsbG8="); // "hello"
+        let mut ctx = HashMap::new();
+        ctx.insert("username".to_string(), vec!["d29ybGQ=".to_string()]); // "world"
+        assert!(!f.evaluate(&ctx));
+    }
+
+    #[test]
+    fn evaluate_matches_any_request_value() {
+        let f = new_func(Aws(AWSUsername), None, "aGVsbG8="); // "hello"
+        let mut ctx = HashMap::new();
+        ctx.insert("username".to_string(), vec!["d29ybGQ=".to_string(), "aGVsbG8=".to_string()]);
+        assert!(f.evaluate(&ctx));
+    }
+
+    #[test]
+    fn evaluate_missing_key_is_false() {
+        let f = new_func(Aws(AWSUsername), None, "aGVsbG8=");
+        let ctx = HashMap::new();
+        assert!(!f.evaluate(&ctx));
+    }
+
+    #[test]
+    fn evaluate_empty_request_values_is_false() {
+        let f = new_func(Aws(AWSUsername), None, "aGVsbG8=");
+        let mut ctx = HashMap::new();
+        ctx.insert("username".to_string(), vec![]);
+        assert!(!f.evaluate(&ctx));
+    }
+
+    #[test]
+    fn evaluate_matches_multibyte_utf8() {
+        // base64("café") = "Y2Fmw6k=" — exercises multi-byte UTF-8 round trip.
+        let f = new_func(Aws(AWSUsername), None, "Y2Fmw6k=");
+        let mut ctx = HashMap::new();
+        ctx.insert("username".to_string(), vec!["Y2Fmw6k=".to_string()]);
+        assert!(f.evaluate(&ctx));
+    }
+
+    #[test]
+    fn evaluate_matches_any_policy_value() {
+        let f = new_multi_func(Aws(AWSUsername), None, &["aGVsbG8=", "d29ybGQ="]);
+        let mut ctx = HashMap::new();
+        ctx.insert("username".to_string(), vec!["d29ybGQ=".to_string()]);
+        assert!(f.evaluate(&ctx));
+    }
+
+    #[test]
+    fn evaluate_invalid_base64_request_value_fails_closed() {
+        // Malformed base64 in the request must never match, regardless of policy value.
+        let f = new_func(Aws(AWSUsername), None, "aGVsbG8=");
+        let mut ctx = HashMap::new();
+        ctx.insert("username".to_string(), vec!["!!!not-base64!!!".to_string()]);
+        assert!(!f.evaluate(&ctx));
+    }
+
+    #[test]
+    fn evaluate_mixed_valid_and_invalid_request_values_fails_closed() {
+        // A valid matching value alongside an invalid base64 value must still
+        // fail closed — for BinaryEquals, any unparsable request value causes
+        // evaluation to return false even if another request value matches.
+        let f = new_func(Aws(AWSUsername), None, "aGVsbG8="); // "hello"
+        let mut ctx = HashMap::new();
+        ctx.insert("username".to_string(), vec!["aGVsbG8=".to_string(), "!!!not-base64!!!".to_string()]);
+        assert!(!f.evaluate(&ctx));
+
+        // Order-independent: invalid first, valid second — still false.
+        let mut ctx2 = HashMap::new();
+        ctx2.insert("username".to_string(), vec!["!!!not-base64!!!".to_string(), "aGVsbG8=".to_string()]);
+        assert!(!f.evaluate(&ctx2));
+    }
+
+    #[test]
+    fn evaluate_raw_request_value_does_not_match() {
+        // A raw (non-base64) request value that happens to equal the decoded
+        // policy bytes must NOT match — both sides are decoded first. "hello"
+        // is not valid standard base64 (length 5, not a multiple of 4), so
+        // decoding fails and the evaluation fails closed.
+        let f = new_func(Aws(AWSUsername), None, "aGVsbG8="); // decodes to "hello"
+        let mut ctx = HashMap::new();
+        ctx.insert("username".to_string(), vec!["hello".to_string()]);
+        assert!(!f.evaluate(&ctx));
+    }
+
+    #[test]
+    fn try_from_constructs_binary_func_value() {
+        // Ergonomic alternatives to BinaryFuncValue::new — parity with the
+        // prior public-struct API and idiomatic Rust conversion.
+        let from_str: BinaryFuncValue = "aGVsbG8=".try_into().unwrap();
+        let from_string: BinaryFuncValue = String::from("aGVsbG8=").try_into().unwrap();
+        assert_eq!(from_str, from_string);
+        assert_eq!(BinaryFuncValue::try_from("!!!bad!!!").unwrap_err(), BinaryFuncValueError::InvalidBase64,);
+    }
+
+    #[test]
+    fn evaluate_all_key_values_must_match() {
+        // Two key/value pairs — both must be satisfied.
+        let f = BinaryFunc {
+            0: vec![
+                FuncKeyValue {
+                    key: Key {
+                        name: Aws(AWSUsername),
+                        variable: None,
+                    },
+                    values: BinaryFuncValue::new("aGVsbG8=").unwrap(), // "hello"
+                },
+                FuncKeyValue {
+                    key: Key {
+                        name: Aws(AWSPrincipalType),
+                        variable: None,
+                    },
+                    values: BinaryFuncValue::new("d29ybGQ=").unwrap(), // "world"
+                },
+            ],
+        };
+
+        let mut ctx = HashMap::new();
+        ctx.insert("username".to_string(), vec!["aGVsbG8=".to_string()]);
+        ctx.insert("principaltype".to_string(), vec!["d29ybGQ=".to_string()]);
+        assert!(f.evaluate(&ctx));
+
+        // Second key missing — must fail.
+        let mut ctx2 = HashMap::new();
+        ctx2.insert("username".to_string(), vec!["aGVsbG8=".to_string()]);
+        assert!(!f.evaluate(&ctx2));
+    }
+
+    #[test]
+    fn deserializes_from_policy_json() {
+        let json = r#"{"aws:username": "aGVsbG8="}"#;
+        let f: BinaryFunc = serde_json::from_str(json).unwrap();
+        let mut ctx = HashMap::new();
+        ctx.insert("username".to_string(), vec!["aGVsbG8=".to_string()]);
+        assert!(f.evaluate(&ctx));
+    }
+
+    #[test]
+    fn deserializes_array_from_policy_json() {
+        let json = r#"{"aws:username": ["aGVsbG8=", "d29ybGQ="]}"#;
+        let f: BinaryFunc = serde_json::from_str(json).unwrap();
+        let mut ctx = HashMap::new();
+        ctx.insert("username".to_string(), vec!["d29ybGQ=".to_string()]);
+        assert!(f.evaluate(&ctx));
+    }
+
+    #[test]
+    fn deserialize_rejects_invalid_base64_at_parse_time() {
+        // Malformed policies must be rejected eagerly, not silently fail at eval.
+        let json = r#"{"aws:username": "!!!not-base64!!!"}"#;
+        let err = serde_json::from_str::<BinaryFunc>(json).unwrap_err();
+        let msg = err.to_string();
+        assert!(msg.contains("invalid base64"), "unexpected error message: {msg}");
+    }
+
+    #[test]
+    fn deserialize_rejects_invalid_base64_in_array_at_parse_time() {
+        let json = r#"{"aws:username": ["aGVsbG8=", "!!!not-base64!!!"]}"#;
+        let err = serde_json::from_str::<BinaryFunc>(json).unwrap_err();
+        let msg = err.to_string();
+        assert!(msg.contains("invalid base64"), "unexpected error message: {msg}");
+    }
+
+    #[test]
+    fn deserialize_rejects_empty_array() {
+        let json = r#"{"aws:username": []}"#;
+        let err = serde_json::from_str::<BinaryFunc>(json).unwrap_err();
+        let msg = err.to_string();
+        assert!(msg.contains("empty"), "unexpected error message: {msg}");
+    }
+
+    #[test]
+    fn serialize_round_trip_preserves_encoded_form() {
+        let json = r#"{"aws:username":"aGVsbG8="}"#;
+        let f: BinaryFunc = serde_json::from_str(json).unwrap();
+        let out = serde_json::to_string(&f).unwrap();
+        assert_eq!(out, json);
+    }
+
+    #[test]
+    fn serialize_round_trip_preserves_encoded_array_form() {
+        let json = r#"{"aws:username":["aGVsbG8=","d29ybGQ="]}"#;
+        let f: BinaryFunc = serde_json::from_str(json).unwrap();
+        let out = serde_json::to_string(&f).unwrap();
+        assert_eq!(out, json);
     }
 }